Projection device and projection system

ABSTRACT

A projection device to magnify and project, on a screen, an image displayed at an image display element, includes: a dioptric system including at least one positive lens and at least one negative lens; and a reflection optical system having at least one reflection optical element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/742,967, filed Jun. 18, 2015, which is based on and claims prioritypursuant to 35 U.S.C. §119 to Japanese Patent Application Nos.2014-128676, filed on Jun. 23, 2014, and 2015-018000, filed on Jan. 30,2015, in the Japan Patent Office, the disclosure of each of which ishereby incorporated by reference in their entirety.

BACKGROUND

Technical Field

The present invention relates to a projection device to magnify andproject an image displayed at an image display element on a projectionsurface such as a screen, and a projection system including theprojection device.

Background Art

A projection device illuminates a display screen of an image displayelement referred to as a light valve such as a Digital MicromirrorDevice (abbreviated as DMD) and a Liquid Chrystal Panel, and projects amagnified image displayed at the image display element on a screenforming the projection surface by a projection optical system.

Especially in recent years, there is a growing demand for a frontprojection projector having an ultra-short projection distance by whicha large-size image can be displayed with a short projection distance. Asa unit having a compact size and achieving such an ultra-shortprojection distance, there are technologies proposed in, for example,JP-2007-079524-A, JP-2009-251458-A, JP-2011-242606-A, andJP-2009-216883-A, in which a dioptric system and a curved mirror arecombined.

Recently, higher luminance is strongly demanded even in such anultra-short throw projector. It is thus also desired to sufficientlyconsider temperature characteristics of the optical system, due to heatfrom a lamp or a light source, and heat generated through absorbingbeams.

Particularly, since a projection angle is large in the ultra-short throwprojector, a focus depth has only a few centimeters or so in aperiphery, particularly at a point most distant from an optical axiswhich is the axis shared by the dioptric system. That is, the focusdepth is extremely narrowed in the ultra-short throw projector, comparedto the front projection projectors not having an ultra-short projectiondistance. Accordingly, the ultra-short projector tends to suffer fromdegradation in resolution as a focus position is largely deviated in theperiphery of a screen, due to an imaging surface curvature caused by theabove-mentioned temperature increase.

However, nothing is disclosed about correcting the imaging surfacecurvature caused by temperature increase in the above-listedJP-2007-079524-A, JP-2009-251458-A, JP-2011-242606-A, andJP-2009-216883-A, and the technologies are insufficient in the case ofconsidering the specifications of the recent projectors.

SUMMARY

Example embodiments of the present invention include: a projectiondevice to magnify and project, on a screen, an image displayed at animage display element, the projection device including: a dioptricsystem including at least one positive lens P1 and at least one negativelens N1; and a reflection optical system having at least one reflectionoptical element. The at least one positive lens P1 and the at least onenegative lens N1 satisfy the conditional expressions (1) and (2):

−6<dnT  (1)

70<vd  (2)

where dnT denotes a temperature coefficient of a relative refractiveindex at a D line in a range of 40 to 60 degrees, and vd denotes an Abbenumber.

Example embodiments of the present invention include: a projectiondevice to magnify and project, on a screen, an image displayed at animage display element, the projection device including:

a dioptric system including at least one cemented lens; and

a reflection optical system having a reflection optical elementincluding at least one magnification, wherein the cemented lens includesat least one positive lens P1 and at least one negative lens N1satisfying the conditional expressions (7), (8), (9), and (10):

4<dnTP  (7)

0.61<θgFP  (8)

3<dnTN  (9)

0.59<θgFN  (10)

where

dnTP denotes a temperature coefficient of a relative refractive index inan e line in a range of 40 to 60 degrees of the positive lens P1,

θgFP denotes a partial dispersion ratio in a g line and an F line of thepositive lens P1,

dnTN denotes a temperature coefficient of a relative refractive index inthe e line in a range of 40 to 60 degrees of the negative lens N1,

θgFN denotes a partial dispersion ratio of the negative lens N1, and

θgf denotes a partial dispersion ratio, expressed by an expression:θgf=(Ng−NF)/(NF−NC), where

Ng denotes a refractive index relative to the g line,

NF denotes a refractive index relative to the F line, and

NC denotes a refractive index relative to a C line.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages and features thereof can be readily obtained and understoodfrom the following detailed description with reference to theaccompanying drawings, wherein:

FIG. 1 is a cross-sectional view illustrating a configuration of aprojection device together with an optical path according to a firstexample of a first embodiment of the present invention;

FIG. 2 is an explanatory diagram illustrating a positional relationbetween an optical axis and a center of an image forming unit in whichan image is formed, when the image forming unit is shifted in aY-direction by a predetermined amount relative to the optical axis;

FIGS. 3A and 3B are cross-sectional views illustrating moving positionsof a focusing lens for respective projection sizes of a projectionoptical system used in the projection device according to the firstexample of the first embodiment of the present invention, and FIG. 3Aillustrates a case where the projection size is a long distance side (80inches) and FIG. 3B illustrates a case where the projection size is ashort distance side (48 inches);

FIG. 4 is an explanatory diagram illustrating field angle numbers(evaluation points) in an image display area virtually displayed on animage display element by setting, as an origin point, a lens opticalaxis of a dioptric system out of the projection optical system accordingto the first example of the first embodiment of the present invention;

FIG. 5 is a diagram illustrating a spot diagram on a screen (in the caseof 80 inches) for light emitted from respective evaluation pointsillustrated in FIG. 4;

FIG. 6 is a diagram illustrating the spot diagram on the screen (in thecase of 60 inches) for the light emitted from the respective evaluationpoints illustrated in FIG. 4;

FIG. 7 is a diagram illustrating the spot diagrams on the screen (in thecase of 48 inches) for the light emitted from the respective evaluationpoints illustrated in FIG. 4;

FIG. 8 is a cross-sectional view illustrating a configuration of aprojection device together with an optical path according to a secondexample of the first embodiment of the present invention;

FIGS. 9A and 9B are cross-sectional views illustrating moving positionsof a focusing lens for respective projection sizes of a projectionoptical system used in the projection device according to the secondexample of the first embodiment of the present invention, and FIG. 9Aillustrates a case where the projection size is a long distance side(100 inches) and FIG. 9B illustrates a case where the projection size isa short distance side (60 inches);

FIG. 10 is a diagram illustrating a spot diagram on a 100-inch screenfor respective evaluation points (respective field angles) illustratedin FIG. 4 in the projection device according to the second example ofthe first embodiment;

FIG. 11 is a diagram illustrating the spot diagram on a 80-inch screenfor the respective evaluation points (respective field angles)illustrated in FIG. 4 in the projection device according to the secondexample of the first embodiment;

FIG. 12 is a diagram illustrating the spot diagram on a 60-inch screenfor the respective evaluation points (respective field angles)illustrated in FIG. 4 in the projection device according to the secondexample of the first embodiment;

FIG. 13 is a cross-sectional view illustrating a configuration of aprojection device together with an optical path according to a firstexample of a second embodiment of the present invention;

FIG. 14 is an explanatory diagram illustrating a positional relationbetween an optical axis and a center of an image forming unit in whichan image is formed, when the image forming unit is shifted inY-direction by a predetermined amount relative to the optical axis;

FIG. 15A and FIG. 15B are cross-sectional views illustrating movingpositions of a focusing lens for respective projection sizes of aprojection optical system used in the projection device according to thefirst example of the second embodiment of the present invention, andFIG. 15A illustrates a case where the projection size is a long distanceside (100 inches), and FIG. 15B illustrates a case where the projectionsize is a short distance side (80 inches);

FIG. 16 is a characteristics diagram illustrating a relation between aheight from an optical axis of a double-sided aspheric negative meniscuslens included in a third lens group in the first example of the secondembodiment and a magnification difference under environment of a roomtemperature 40 degrees;

FIG. 17 is an explanatory diagram illustrating field angle numbers(evaluation points) in an image display area virtually displayed on animage display element by setting, as an origin point, a lens opticalaxis of a dioptric system out of the projection optical system accordingto the first example of the second embodiment of the present invention;

FIG. 18 is a diagram illustrating a spot diagram on a screen (in thecase of 100 inches) for light emitted from respective evaluation pointsillustrated in FIG. 17;

FIG. 19 is a diagram illustrating the spot diagram on the screen (in thecase of 80 inches) for the light emitted from the respective evaluationpoints illustrated in FIG. 17;

FIG. 20 is a diagram illustrating the spot diagrams on the screen (inthe case of 60 inches) for the light emitted from the respectiveevaluation points illustrated in FIG. 17;

FIG. 21 is a diagram illustrating the spot diagram on the screen (in thecase of 100 inches) for the light emitted from the respective evaluationpoints illustrated in FIG. 17 when the temperature is increased by 20more degrees from the room temperature (20 degrees);

FIG. 22 is a diagram illustrating the spot diagram on the screen (in thecase of 80 inches) for the light emitted from the respective evaluationpoints illustrated in FIG. 17 when the temperature is increased by 20more degrees from the room temperature (20 degrees);

FIG. 23 is a diagram illustrating the spot diagram on the screen (in thecase of 60 inches) for the light emitted from the respective evaluationpoints illustrated in FIG. 17 when the temperature is increased by 20more degrees from the room temperature (20 degrees);

FIG. 24 is a cross-sectional view illustrating a configuration of aprojection device together with an optical path according to a secondexample of a second embodiment of the present invention;

FIGS. 25A and 25B are cross-sectional views illustrating movingpositions of a focusing lens for respective projection sizes of aprojection optical system used in the projection device according to thesecond example of the second embodiment of the present invention, andFIG. 25A illustrates a case of a long distance side (100 inches), andFIG. 25B illustrates a case of a short distance side (80 inches);

FIG. 26 is a characteristics diagram illustrating a relation between aheight from an optical axis of a double-sided aspheric negative meniscuslens included in a third lens group in the second example of the secondembodiment and a magnification difference under environment of the roomtemperature 40 degrees;

FIG. 27 is a diagram illustrating a spot diagram on a 100-inch screenfor respective evaluation points (respective field angles) illustratedin FIG. 17 in the projection device according to the second example ofthe second embodiment;

FIG. 28 is a diagram illustrating the spot diagram on a 80-inch screenfor the respective evaluation points (respective field angles)illustrated in FIG. 17 in the projection device according to the secondexample of the second embodiment;

FIG. 29 is a diagram illustrating the spot diagram on a 60-inch screenfor the respective evaluation points (respective field angles)illustrated in FIG. 17 in the projection device according to the secondexample of the second embodiment;

FIG. 30 is a diagram illustrating the spot diagram on the 100-inchscreen for the respective evaluation points (respective field angles)illustrated in FIG. 17 in the projection device according to the secondexample of the second embodiment;

FIG. 31 is a diagram illustrating the spot diagram on the 80-inch screenfor the respective evaluation points (respective field angles)illustrated in FIG. 17 in the projection device according to the secondexample of the second embodiment; and

FIG. 32 is a diagram illustrating the spot diagram on the 60-inch screenfor the respective evaluation points (respective field angles)illustrated in FIG. 17 in the projection device according to the secondexample of the second embodiment.

The accompanying drawings are intended to depict example embodiments ofthe present invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION OF THE INVENTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“includes” and/or “including”, when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In describing example embodiments shown in the drawings, specificterminology is employed for the sake of clarity. However, the presentdisclosure is not intended to be limited to the specific terminology soselected and it is to be understood that each specific element includesall technical equivalents that operate in a similar manner.

Referring now to FIGS. 1 to 12, a projection device and a projectionsystem including the projection device will be described according to afirst embodiment of the present invention.

Before describing specific examples, concept of the first embodiment ofthe present invention will be described.

The present invention is a projection device that magnifies andprojects, on a screen, an image displayed at an image display element.The projection device includes a dioptric system, and a reflectionoptical system having at least one reflection optical element. Thedioptric system includes at least one positive lens P1 and one negativelens N1, and the positive lens P1 and the negative lens N1 satisfyfollowing conditional expressions (1) and (2):

−6<dnT  (1)

70<vd  (2)

dnT denotes a temperature coefficient of a relative refractive index ata D line in a range of 40 to 60 degrees and vd is an Abbe number.

When glass material of the positive lens P1 and the negative lens N1satisfy the conditional expression (1), not only change of a focallength caused by temperature increase can be corrected by the two lensesbut also particularly change of imaging surface curvature can be highlycorrected. As a result, good resolution can be obtained in every detailin the ultra-short throw projector despite occurrence of temperatureincrease. Further, temperature compensation can be performed bysatisfying the conditional expression (1), but this is not sufficientfor aberration correction, especially, chromatic aberration correction.Both optical performance and temperature characteristics can be achievedonly after the conditional expression (2) is satisfied at the same time.More preferably, following conditional expressions (1′) and (2′) aresatisfied as well:

−5<dnT  (1′)

72<vd  (2′)

More preferably, the positive lens P1 is disposed closer to an imagedisplay element side than an aperture stop is, and the negative lens N1is disposed closer to a magnification side than an aperture stop is. Bydisposing the lenses as described above, aberration correction can beeffectively performed. Further, the “aperture stop” herein indicates aplace where the thickness of a luminous flux (entire luminous flux)passing the dioptric system from an entire area of the image displayelement becomes thinnest.

More favorably, the positive lens P1 and the negative lens N1 areincluded in a lens group including a lens having highest temperature ata time of displaying a white image. By disposing the lenses in that lensgroup, a projection optical system having favorable temperaturecharacteristics can be obtained.

More favorably, the positive lens P1 and the negative lens N1 areincluded in a lens group closest to the image display element side, forexample, in a first lens group. By disposing the lenses in that lensgroup, a projection optical system having favorable temperaturecharacteristics can be obtained.

More favorably, the positive lens P1 and the negative lens N1 areincluded in a lens group not moved at the time of focusing. This resultsin favorable temperature characteristics in each image size.

More favorably, the dioptric system may include a resin lens, and theresin lens is included in a lens group having lowest temperature at thetime of displaying a white image. By disposing the lens in that lensgroup as described above, the image surface curvature associated withtemperature change can be effectively suppressed.

More favorably, the reflection optical element is a concave mirror, andincludes a free-form surface. By use of the free-form surface,correction of the image surface curvature can be effectively performed.

More favorably, the following conditional expression (3):

TR<0.30  (3)

is satisfied where a ratio of a distance to the screen from anintersection between the concave mirror and an optical axis of thedioptric system, to a lateral width of the screen is TR. By satisfyingthe conditional expression, a projection device having an extremelyshort projection distance can be obtained. More preferably, thefollowing conditional expression (3′):

TR<0.25  (3′)

is satisfied.

More favorably, the following conditional expression (4) is satisfied:

BF/Y<4.0  (4)

where BF denotes a distance from an intersection between a surfaceincluding the image display element and the optical axis to a vertex ofan image display element side surface of a lens closest to the imagedisplay element side, Y denotes a maximum value of a distance betweenthe optical axis and an end portion of an image forming unit, and theoptical axis is an axis shared by a plurality of axisymmetric lenses ofthe dioptric system.

By satisfying the conditional expression (4), the projection opticalsystem can be further downsized. More preferably, the followingconditional expression (4′):

BY/Y<3.5  (4′)

is satisfied.

More favorably, a projection optical system is implemented as anon-telecentric optical system. By employing the non-telecentric opticalsystem, there is an advantage in downsizing.

With the above described configurations, the projection optical systemcan provide a projection device having an extremely short projectiondistance, achieving higher luminance, formed in a compact size, havinghigh performance and favorable temperature characteristics.

Next, a configuration of a projection optical system of a projectiondevice of the present invention will be described in detail.

FIG. 1 is a cross-sectional view illustrating a configuration of aprojection device together with an optical path according to a firstexample of a first embodiment of the present invention, and FIG. 2 is anexplanatory diagram illustrating a positional relation between anoptical axis and a center of an image forming unit in which an image isformed, when the image forming unit is shifted in a Y-direction by apredetermined amount relative to the optical axis.

FIGS. 3A and 3B are cross-sectional views illustrating moving positionsof a focusing lens in respective projection sizes of a projectionoptical system used in the projection device according to the firstexample of the first embodiment of the present invention, and FIG. 3Aillustrates a case where the projection size is a long distance side (80inches) and FIG. 3B illustrates a case where the projection size is ashort distance side (48 inches).

In FIG. 1, a reference sign LV indicates an image forming unit. Theimage forming unit LV is, more specifically, a light valve such as a“digital micro-mirror device (abbreviated as DMD)”, a “transmissiveliquid crystal panel”, and a “reflective liquid crystal panel”, and aportion indicated by the reference sign LV is a “portion where an imageto be projected is formed”. In the case where the image forming unit LVdoes not have a function to emit light by itself like the DMD, imageinformation formed at the image forming unit LV is illuminated byillumination light from an illumination optical system LS. For theillumination optical system LS, a system having a function toeffectively illuminate the image forming unit LV is preferable. Further,for example, a rod integrator and a fly-eye integrator can be used inorder to have uniform illumination. Further, for a light source of theillumination, a white light source such as a super-high pressure mercurylamp, a xenon lamp, a halogen lamp, or a light-emitting diode (LED) canbe used. Further, a monochromatic light source such as a monochromaticLED and a laser diode (LD) can be also used. A known technology isadopted as the illumination optical system. Therefore, description of aspecific example is omitted here.

In the present embodiment, the DMD is assumed as the image forming unitLV. Further, the present embodiment has a precondition that “the imageforming unit does not have a function to emit light” by itself, but animage forming unit including “a self-light emitting system having afunction to cause a generated image to emit light” can also be used.

A parallel plate F disposed in the vicinity of the image forming unit LVis assumed to be a cover glass (seal glass) of the image forming unitLV. A reference sign H represents an outer surface of the projectiondevice, and a reference sign S represents a stop position (aperturestop). Further, a reference sign SC in FIG. 1 represents a screen.

FIG. 1 illustrates an optical path diagram in the case of 48 inches inwhich a front lens element is most protruded. As illustrated in FIG. 1,an axis shared by a plurality of axisymmetric lenses is defined as anaxis A, a direction parallel to the axis A is defined as Z-axisdirection, an axis vertical to the axis A within a surface including abeam emitted from a center of the image display element and passing acenter of the stop S is defined as a Y-axis, and an axis vertical to theaxis A and the Y-axis is defined as an X-axis. In FIG. 1, a clockwiserotary direction is defined as +a direction.

A luminous flux having intensity two-dimensionally modulated with theimage information at the DMD is to be a projected luminous flux asobject light. The projected luminous flux from the image forming unit LVpasses a dioptric system 11, a folding mirror 12, and a free-formsurface concave mirror 13, and becomes an imaging luminous flux. Inother words, an image formed on the DMD (image forming unit LV) ismagnified and projected on the screen SC by the projection opticalsystem, and becomes a projection image. Here, a surface on which theimage is formed is defined as an image forming surface. Respectiveoptical elements in the dioptric system 11 share an optical axisindividually, and the image forming unit LV is shifted in theY-direction relative to the optical axis A as illustrated in FIG. 2.

According to the first embodiment, the system is formed by using thedioptric system 11, and a reflection optical system such as the foldingmirror 12 and the one free-form surface concave mirror 13. The number ofmirrors may be increased, but this is not so preferable because theconfiguration may become complex and upsized, and cost increase may becaused as well.

Heat generation by absorbing heat and light from a power source and alamp is increased in the illumination optical system LS along withenhancement of higher luminance. Particularly, in the projector usingthe non-telecentric optical system, a light absorption amount to a lensbarrel is largely increased by shortening back focus for downsizing.Therefore, a lens group closest to an image display side has thetemperature easily increased, and temperature compensation is neededinside the lens group.

Considering above, in the first example in the first embodiment, changeof a focal length and expansion of a mechanical holder due to heat arebalanced by using glass material satisfying conditional expressions (1)and (2) (for example, S-FPM3 having nd: 1.53775, vd: 74.7031, and DnT:−4.4 of OHARA INC.,) for each of a positive lens closest to the imagedisplay element side, a positive lens and a negative lens across thestop. Further, in addition to the above, an aspheric surface lens isadopted for the positive lens closest to the image display element side,so that temperature change at image surface curvature can be more highlyadjusted.

Moreover, by appropriately disposing a cooling mechanism, temperaturechange can be suppressed for the lens group having the aspheric surfacelens and moved at the time of focusing, and temperature change at theimage surface curvature can be suppressed.

The light having passed the dioptric system 11 forms, as a space image,an intermediate image on a side closer to the image forming unit LV thana reflection mirror. The intermediate image is conjugate to the imageinformation formed on the image forming unit LV. The intermediate imageis not necessarily imaged as a planar image, and formed as a curvedimage in the first embodiment and other embodiments. The intermediateimage is magnified and projected by the free-form surface concave mirror13 disposed closest to a magnification side, and screened on the screenSC. The intermediate image includes image surface curvature anddistortion, but the curvature and distortion can be corrected by usingthe free-form surface concave mirror 13. Therefore, a lens system has areduced burden to perform aberration correction, thereby increasingfreedom of design and having an advantage in downsizing, for example.Here, the free-form surface referred is an anamorphic surface in whichX-direction curvature corresponding to an X-direction position in anoptional Y-direction position is not constant, and Y-direction curvaturecorresponding to a Y-direction position in an optional X-directionposition is not constant.

Preferably, a dust-proof glass 14 is disposed between the free-formsurface concave mirror 13 and the screen SC. According to the presentfirst embodiment, a flat plate glass is used as the dust-proof glass 14,but the glass may also have curvature, or may be an optical elementhaving a magnification such as a lens. Further, the duct-proof glass isdisposed tilted to the axis A instead of being vertical, but the angleis optional and may be vertical to the axis A.

First Example

Next, the first example of the present invention will be described indetail with reference to FIG. 3.

The reference signs in the first example and a later-described secondexample are defined as follows.

f: focal length in entire system

NA: numerical aperture

ω: half field angle (deg)

R: curvature radius (paraxial curvature radius on the aspheric surface)

D: surface distance

Nd: refractive index

vd: Abbe number

K: conic constant of aspheric surface

Ai: i-th aspheric surface coefficient

Cj: free-form surface coefficient

The shape of the aspheric surface is expressed by a following knownexpression (5) by setting X as an amount of the aspheric surface in anoptical axis direction, defining an inverse of paraxial curvature radius(paraxial curvature) as C, a height from the optical axis as H, and aconic constant as K, and using the above-mentioned aspheric surfacecoefficient of each degree.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{X = {\frac{C \cdot H^{2}}{1 + \sqrt{\left\{ {1 - {\left( {1 + K} \right) \cdot C^{2} \cdot H^{2}}} \right\}}} + {\sum\limits_{i = 1}{{Ai} \cdot H^{i}}}}} & (5)\end{matrix}$

The shape is specified by providing the paraxial curvature radius, theconic constant, and the aspheric surface coefficient.

Further, the shape of the free-form surface is specified by a followingknown expression (6) by setting X as an amount of the free-form surfacein the optical axis direction, defining an inverse number of paraxialcurvature radius (paraxial curvature) as C, a height from the opticalaxis as H, and a conic constant as K, and using the above-mentionedfree-form surface coefficient.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack & \; \\{X = {\frac{C \cdot H^{2}}{1 + \sqrt{\left\{ {1 - {\left( {1 + K} \right) \cdot C^{2} \cdot H^{2}}} \right\}}} + {\sum\limits_{j = 1}{{{Cj} \cdot x^{m}}y^{n}}}}} & (6)\end{matrix}$

However, there is a following condition.

$j = {\frac{\left( {m + n} \right)^{2} + m + {3n}}{2} + 1}$

The shape of the free-form surface is specified by providing theparaxial curvature radius, the conic constant, and the free-form surfacecoefficient.

As illustrated in FIG. 1, an axis in a normal direction of the imageforming unit and parallel to the axis A that is the axis shared byaxisymmetric lenses is defined as the Z-axis. Among the axes within thesurface including the beam emitted from the center of the image displayelement and passing the center of the stop, an axis vertical to the axisA is defined as the Y-axis. An axis vertical to the axis A and theY-axis is defined as the X-axis. In FIG. 1, the clockwise rotarydirection is defined as +a direction.

FIG. 3 illustrates a lens configuration of the dioptric system and afocusing state according to the first example of the first embodiment ofthe present invention. In this dioptric system, a first lens group G1having positive refractive power, a second lens group G2 having positiverefractive power, a third lens group G3 having negative refractivepower, and a fourth lens group G4 having positive refractive power arearranged in order from an image forming unit side to a magnificationside. In performing focusing in response to change of a projectiondistance, the positive second lens group G2 and the negative third lensgroup G3 are moved to the image forming unit side, and the positivefourth lens group G4 is moved to the magnification side, at the time offocusing from the long distance side (80 inches) to the short distanceside (48 inches).

The first lens group G1 includes, in order from the image forming unitLV side, a first lens L1 formed of a double-sided aspheric biconvex lensin which a convex surface having larger curvature than the magnificationside is oriented to the image forming unit side, a second lens L2 formedof a positive meniscus lens in which a convex surface is oriented to themagnification side, a third lens L3 formed of a negative meniscus lensin which a convex surface is oriented to the image forming unit side, acemented lens including a fourth lens L4 formed of a negative meniscuslens in which a convex surface is oriented to the image forming unitside and a fifth lens L5 formed of a positive meniscus lens in which aconvex surface is oriented to the image forming unit side, an aperturestop S, a sixth lens L6 formed of a negative meniscus lens in which aconvex surface is oriented to the magnification side, a seventh lens L7formed of a double-sided aspheric biconvex lens in which a convexsurface having larger curvature than the image forming unit side isoriented to the magnification side, an eighth lens L8 formed of anegative meniscus lens in which a convex surface is oriented to theimage forming unit side, a cemented lens including a ninth lens L9formed of a biconvex lens in which a convex surface having largercurvature than the image forming unit side is oriented to themagnification side and a tenth lens L10 formed of a biconcave lens inwhich a concave surface having larger curvature than the magnificationside is oriented to the image forming unit side, and an eleventh lensL11 formed of a biconvex lens in which a convex surface having largercurvature than the image forming unit side is oriented to themagnification side. The second lens group G2 includes one twelfth lensL12 formed of a positive meniscus lens in which a convex surface isoriented to the image forming unit side. The third lens group G3includes a thirteenth lens L13 formed of a biconcave lens in which aconcave surface having curvature larger than the image forming unit isoriented to the magnification side, a fourteenth lens L14 formed of aplano-concave lens having a flat surface at the magnification side, anda fifteenth lens L15 formed of a double-sided aspheric negative meniscuslens in which a convex surface is oriented to the image forming unitside. The fourth lens group G4 includes a sixteenth lens L16 formed of adouble-sided aspheric positive meniscus lens in which a convex surfaceis oriented to the magnification side.

The dioptric system is formed of the above lens groups, and a foldingmirror 12 (surface 34) and a free-form surface concave mirror 13(surface 35) are disposed at the magnification side thereof.

Note that the first lens L1 and the fifth lens L5 are referred to aspositive lens P1, and the sixth lens L6 is referred to as negative lensN1.

Hereinafter, lens data is listed in TABLE 1. In the TABLE 1, a surfacenumber attached with * is the aspheric surface, and a surface numberattached with ** is the free-form surface.

TABLE 1 NUMERICAL APERTURE: 0.200 R D Nd vd GLASS MATERIAL  1 ∞ 1.00  2∞ 1.00 1.51633 64.1420 S-BSL7 OHARA  3 ∞ 28.00   4* 14.540 4.20 1.5377574.7031 S-FPM3 OHARA  5 −66.951 1.50  6 −27.955 2.25 1.58913 61.1526L-BAL35 OHARA  7 −24.919 0.30  8 61.206 1.00 1.76200 40.1002 S-LAM55OHARA  9 20.058 0.30 10 15.427 0.80 1.90366 31.3150 TAFD25 HOYA 11 9.7502.66 1.53775 74.7031 S-FPM3 OHARA 12 20.974 1.36 STOP ∞ 2.45 13 −21.1180.60 1.53775 74.7031 S-FPM3 OHARA 14 −39.217 2.64 15* 25.408 4.681.58913 61.1526 L-BAL35 OHARA 16* −20.601 0.30 17 40.902 0.80 1.6228057.0527 S-BSM10 OHARA 18 21.739 2.09 19 202.603 6.92 1.85478 24.7990S-NBH56 OHARA 20 −13.233 1.00 1.91650 31.6041 S-LAH88 OHARA 21 31.57414.44  22 57.162 10.71  1.49700 81.5459 S-FPL51 OHARA 23 −48.198VARIABLE DA 24 41.474 7.01 1.80100 34.9674 S-LAM66 OHARA 25 238.171VARIABLE DB 26 −169.741 1.20 1.85478 24.7990 S-NBH56 OHARA 27 161.2028.88 28 −35.153 1.80 1.83481 42.7253 S-LAH55V OHARA 29 ∞ 0.30 30* 60.4383.00 1.53046 55.8000 RESIN 31* 31.695 VARIABLE DC 32* −29.909 5.301.53046 55.8000 RESIN 33* −27.268 VARIABLE DD 34 ∞ −83.91  REFLECTIONSURFACE 35** ∞ VARIABLE DE REFLECTION SURFACE

That is, in TABLE 1, optical surfaces of a fourth surface, a fifthsurface, a fifteenth surface, a sixteenth surface, a thirtieth surface,a thirty-first surface, a thirty-second surface, and a thirty-thirdsurface attached with “*” are the aspheric surfaces, and parameters ofthe respective aspheric surfaces in the expression (5) are as shown innext TABLE 2.

Note that “En” is “exponent of 10”, that is, “×10^(n)” in the asphericsurface coefficient. For example, “E-05” represents “×10⁻⁵”

TABLE 2 ASPHERIC SURFACE COEFFICIENTS K A4 A6 A8 4TH 0.1783 −2.9102E−05−1.1652E−08 SURFACE 5TH −64.9202 1.9295E−05 1.8481E−07 SURFACE 15TH1.2261 −2.1678E−05 −5.2896E−08 SURFACE 16TH −1.3435 9.7955E−06−3.9413E−08 SURFACE 30TH 0.9126 −2.8961E−05 2.2669E−08 1.1944E−10SURFACE 31TH −4.2646 −4.3867E−05 8.2194E−08 −1.1309E−10 SURFACE 32TH−0.7468 −1.8382E−05 7.4940E−10 −4.3494E−12 SURFACE 33TH −1.0966−1.5990E−05 −1.1268E−08 4.7986E−11 SURFACE A10 A12 A14 A16 4TH SURFACE5TH SURFACE 15TH SURFACE 16TH SURFACE 30TH −4.9118E−13 8.3740E−16−7.14034E−19 2.47551E−22 SURFACE 31TH 8.9692E−14 −3.3502E−17 SURFACE32TH 1.4576E−13 −2.0156E−16 8.25756E−20 SURFACE 33TH −1.5373E−134.1252E−16 −4.44079E−19 1.65614E−22 SURFACE

DA, DB, DC, DD, and DE in TABLE 1 represent variable distances.

Among the distances, the variable distance DA is a distance between thefirst lens group G1 and the second lens group G2, namely, the variabledistance between a surface 23 and a surface 24. The variable distance DBis a distance between the second lens group G2 and the third group G3,namely, the variable distance between a surface 25 and a surface 26. Thevariable distance DC is a distance between the third lens group G3 and afourth lens group G4, namely, the variable distance between a surface 31and a surface 32. The variable distance DD is a distance between thefourth lens group G4 and the folding mirror 12, and DE is the variabledistance between the free-form surface concave mirror 13 and the screensurface SC.

Thus, in the projection optical system, the second lens group G2 and thethird lens group G3 are moved to the image forming unit side, and thefourth lens group G4 is moved to the magnification side, in FIG. 3 atthe time of focusing from the long distance side to the short distanceside to perform focusing in response to the change of the projectiondistance. Thus, by changing a magnifying ratio, focus adjustment isperformed in accordance with the projection sizes of the 48 inches, 60inches, and 80 inches of a diagonal size of the projection image.

The surface distances DA, DB, DC, DD, and DE in which the distancesbetween the lens groups are varied at the time of focus adjustment areindicated as “variable DA”, “variable DB”, “variable DC”, “variable DD”,and “variable DE” in TABLE 1, and as illustrated in next TABLE 3, thesurface distances DA to DE are varied with respect to the diagonal sizes80, 60, and 48 inches of the projection image.

TABLE 3 VARIABLE DISTANCE FOCUSING SHORT LONG DISTANCE STANDARD DISTANCESCREEN SIZE 48 INCHES 60 INCHES 80 INCHES VARIABLE DA 2.00 2.86 3.52VARIABLE DB 5.12 4.93 4.77 VARIABLE DC 24.49 19.55 15.16 VARIABLE DD48.97 53.23 57.12 VARIABLE DE 244.24 297.44 385.38

Further, the shape of the free-form surface is specified by theabove-described expression (6), providing an inverse number of paraxialcurvature radius (paraxial curvature) C, a height from the optical axisH, a conic constant K, and free-form surface coefficients listed in nextTABLE 4 while defining X as an amount of the free-form surface in theoptical axis direction.

TABLE 4 FREE-FORM SURFACE COEFFICIENTS 35TH SURFACE K 0 C4 1.0821E−02 C6−1.1254E−03 C8 1.1482E−04 C10 −2.3053E−04 C11 −9.6864E−07 C13 7.8797E−06C15 −5.2503E−07 C17 −4.5413E−08 C19 1.7411E−07 C21 3.7066E−08 C221.6826E−10 C26 9.8546E−10 C28 4.3972E−10 C30 1.9934E−12 C32 −5.8024E−11C34 −1.2594E−11 C36 −2.2947E−14 C37 −1.9874E−14 C39 1.2852E−13 C41−5.5519E−13 C43 −1.1902E−13 C45 −1.8461E−14 C47 2.7985E−16 C493.2797E−15 C51 −1.2440E−15 C53 7.3482E−16 C55 3.2915E−17 C56 1.7806E−18C58 6.1984E−18 C60 2.3345E−17 C62 7.7410E−18 C64 8.6880E−18 C669.8187E−19

Note that the projection distance and TR take values listed in nextTABLE 5 in accordance with the short distance side, standard, and longdistance side. Here, TR is expressed as:

[a distance to the screen from an intersection between the free-formsurface concave mirror 13 and the axis A]/[a lateral width of thescreen]

TABLE 5 PROJECTION DISTANCE AND TR SHORT DISTANCE STANDARD LONG DISTANCE48 INCHES 60 INCHES 80 INCHES PROJECTION 246.92 300.10 388.02 DISTANCETR 0.232 0.226 0.219

Hereinafter, specific values of the DMD used as the image forming unitLV of the first example and others are shown.

DMD size

Dot size: 7.56 μm

Length in lateral direction: 14.5152 mm

Length in vertical direction: 8.1648 mm

Optical axis to center of device: 5.31 mm

BF/Y: 3.45

Positional coordinates of the folding mirror 12 and free-form surfaceconcave mirror 13 from an apex in a focused state in which theprojection image of the lens positioned closest to a reflection surfaceside is maximized are shown in next TABLE 6. As for rotation, an anglemade by a surface normal and the optical axis is indicated.

TABLE 6 Y-AXIS Z-AXIS α 34TH SURFACE 0.00 57.12 −45.00 35TH SURFACE83.91 79.15 −102.71

Spot diagrams corresponding to respective field angles illustrated inFIG. 4 are illustrated in FIGS. 5 to 7. The respective spot diagramsrepresent imaging characteristics (mm) on the screen with respect towavelengths 625 nm (red), 550 nm (green), and 425 nm (blue). It is clearthat good imaging is performed.

The focal lengths in the entire system and the first lens group in thecase of a room temperature (20 degrees) and the case where thetemperature is increased by 20 more degrees are shown in next TABLE 7.

TABLE 7 20 DEGREES 40 DEGREES ENTIRE SYSTEM 20.63 20.63 FIRST LENS GROUP72.43 72.44

This shows that change of the focal lengths at the time of temperaturechange is suppressed.

Note that values corresponding to the conditional expressions (1) to (4)are as shown below and satisfy the respective conditional expressions(1) to (4) in the case of the first example:

-   -   Conditional expression (1): dnT=−4.4    -   Conditional expression (2): vd=74.7031    -   Conditional expression (3): TR=0.219 to 0.232    -   Conditional expression (4): BF/Y=3.45

Second Example

Next, a projection device according to a second example of the firstembodiment will be described with reference to FIG. 8.

As illustrated in FIG. 8, an axis in a normal direction of an imageforming unit and parallel to an axis A that is an axis shared byaxisymmetric lenses is defined as Z-axis. Among axes within a surfaceincluding a beam emitted from a center of an image display element andpassing a center of a stop S, an axis vertical to the axis A is definedas Y-axis. An axis vertical to the axis A and the Y-axis is defined asX-axis. In FIG. 8, the clockwise rotary direction is defined as +adirection.

FIG. 9 illustrates a lens configuration of a dioptric system and afocusing state according to a second example of the first embodiment ofthe present invention. In this dioptric system, a first lens group G1having positive refractive power, a second lens group G2 having positiverefractive power, a third lens group G3 having negative refractivepower, and a fourth lens group G4 having positive refractive power arearranged in order from an image forming unit side to a magnificationside. As illustrated in FIG. 8, a free-form surface concave mirror 13 isincluded in a position closest to the magnification side, and inperforming focusing in response to change of a projection distance, thepositive second lens group G2 and the negative third lens group G3 aremoved to the image forming unit side, and the positive fourth lens groupG4 is moved to the magnification side, at the time of focusing from along distance side (100 inches) to a short distance side (60 inches).

The first lens group G1 includes, in order from an image forming unit LVside, a first lens L1 formed of a double-sided aspheric biconvex lens inwhich a convex surface having larger curvature than the magnificationside is oriented to the image forming unit side, a second lens L2 formedof a negative meniscus lens in which a convex surface is oriented to theimage forming unit side, a cemented lens including a third lens L3formed of a negative meniscus lens in which a convex surface is orientedto the image forming unit side and a fourth lens L4 formed of a positivemeniscus lens in which a convex surface is oriented to the image formingunit side, an aperture stop S, a fifth lens L5 formed of a negativemeniscus lens in which a convex surface is oriented to the magnificationside, a sixth lens L6 formed of a biconvex lens in which a convexsurface having larger curvature than the image forming unit side isoriented to the magnification side, a seventh lens L7 formed of adouble-sided aspheric surface negative meniscus lens in which a convexsurface is oriented to the image forming unit side, a cemented lensincluding an eighth lens L8 formed of a biconvex lens in which a convexsurface having larger curvature than an image forming surface side isoriented to the magnification side and a ninth lens L9 formed of abiconcave lens in which a concave surface having larger curvature thanthe magnification side is oriented to the image forming unit side, and atenth lens L10 formed of a biconvex lens in which a convex surfacehaving larger curvature than the image forming unit side is oriented tothe magnification side. The second lens group G2 includes one eleventhlens L11 formed of a positive meniscus lens in which a convex surface isoriented to the image forming unit side. The third lens group G3includes a twelfth lens L12 formed of a negative meniscus lens in whicha convex surface is oriented to the image forming unit side, athirteenth lens L13 formed of a biconcave lens in which a concavesurface having larger curvature than the magnification side than theimage forming unit side, and a fourteenth lens L14 formed of adouble-sided aspheric surface negative meniscus lens in which a convexsurface is oriented to the image forming unit side. The fourth lensgroup G4 includes one fifteenth lens L15 formed of a double-sidedaspheric surface positive meniscus lens in which a convex surface isoriented to the magnification side.

A dioptric system is formed of the above lens groups, and a foldingmirror 12 (surface 32) and a free-form surface concave mirror 13(surface 33) are disposed at the magnification side thereof.

Note that the third lens L3 is referred to as positive lens P1, and thefifth lens L5 is referred to as negative lens N1.

Hereinafter, lens data is listed in TABLE 8. In the TABLE 8, a surfacenumber attached with * is the aspheric surface, and a surface numberattached with ** is the free-form surface.

TABLE 8 NUMERICAL APERTURE: 0.200 R D Nd vd GLASS MATERIAL  1 ∞ 1.00  2∞ 1.00 1.51633 64.1420 S-BSL7 OHARA  3 ∞ 28.00   4* 15.425 6.00 1.4970081.5459 S-FPL51 OHARA  5* −77.187 1.79  6 52.890 0.70 1.85478 24.7990S-NBH56 OHARA  7 29.580 1.14  8 15.516 0.80 1.90366 31.3150 TAFD25 HOYA 9 9.940 2.60 1.53775 74.7031 S-FPM3 OHARA 10 20.056 1.44 STOP ∞ 2.55 11−19.611 0.70 1.53775 74.7031 S-FPM3 OHARA 12 −42.699 2.01 13 26.678 4.581.58913 61.1526 L-BAL35 OHARA 14 −19.882 0.30 15* 41.592 0.80 1.8160046.6206 S-LAH59 OHARA 16* 21.739 1.48 17 58.130 6.06 1.85478 24.7990S-NBH56 OHARA 18 −12.870 1.00 1.91650 31.6041 S-LAH88 OHARA 19 27.86017.10  20 75.931 9.74 1.59522 67.7357 S-FPM2 OHARA 21 −48.799 VARIABLEDA 22 37.217 6.17 1.75700 47.8232 S-LAM54 OHARA 23 90.427 VARIABLE DB 24666.346 2.00 1.91650 31.6041 S-LAH88 OHARA 25 75.497 9.76 26 −38.3602.20 1.83481 42.7253 S-LAH55V OHARA 27 964.042 0.30 28* 47.073 3.001.53046 55.8000 RESIN 29* 27.388 VARIABLE DC 30* −34.791 5.30 1.5304655.8000 RESIN 31* −30.585 VARIABLE DD 32 ∞ −82.93  REFLECTION SURFACE33** ∞ VARIABLE DE REFLECTION SURFACE

That is, in TABLE 8, optical surfaces of a fourth surface, a fifthsurface, a fifteenth surface, a sixteenth surface, a twenty-eighthsurface, a twenty-ninth surface, a thirtieth surface, and a thirty-firstsurface attached with “*” are the aspheric surfaces, and parameters ofthe respective aspheric surfaces in the expression (5) are as shown innext TABLE 9.

Note that “En” is “exponent of 10”, that is, “×10^(n)” in the asphericsurface coefficient. For example, “E-05” represents “×10⁻⁵”.

TABLE 9 ASPHERIC SURFACE COEFFICIENTS K A4 A6 A8 4TH 0.1378 −2.0241E−05SURFACE 5TH −78.3049 2.1652E−05 1.4060E−07 SURFACE 15TH 1.7996−2.3606E−05 −6.0352E−08 SURFACE 16TH −1.0833 1.2898E−05 −4.7269E−08SURFACE 28TH −4.2758 −2.2742E−05 −2.7249E−08 3.2226E−10 SURFACE 29TH−1.6081 −5.5024E−05 8.3205E−08 −7.5460E−11 SURFACE 30TH −0.2509−3.4657E−05 4.9250E−08 −1.3282E−10 SURFACE 31TH −0.7157 −2.6314E−051.8397E−08 −2.4843E−11 SURFACE A10 A12 A14 A16 4TH SURFACE 5TH SURFACE15TH SURFACE 16TH SURFACE 28TH −9.0197E−13 1.2636E−15 −9.26832E−192.87074E−22 SURFACE 29TH 2.3101E−14 SURFACE 30TH 3.8358E−13 −4.1608E−161.5424E−19 SURFACE 31TH −6.1850E−14 4.0889E−16 −5.11951E−19 1.97594E−22SURFACE

DA, DB, DC, DD, and DE in TABLE 8 represent variable distances.

Among the distances, the variable distance DA is a distance between thefirst lens group G1 and the second lens group G2, namely, the variabledistance between a surface 21 and a surface 22. The variable distance DBis a distance between the second lens group G2 and the third group G3,namely, the variable distance between a surface 23 and a surface 24. Thevariable distance DC is a distance between the third lens group G3 and afourth lens group G4, namely, the variable distance between a surface 29and a surface 30.

The variable distance DD is a distance between the fourth lens group G4and the folding mirror 12, and DE is the variable distance between thefree-form surface concave mirror 13 and a screen surface SC.

Thus, in a projection optical system, the second lens group G2 and thethird lens group G3 are moved to the image forming unit side, and thefourth lens group G4 is moved to the magnification side in FIG. 9 at thetime of focusing from the long distance side to the short distance sideto perform focusing in response to the change of the projectiondistance. Thus, by changing a magnifying ratio, focus adjustment isperformed in accordance with the projection sizes of the 60 inches, 80inches, and 100 inches of a diagonal size of a projection image.

The surface distances DA, DB, DC, DD, and DE in which the distancesbetween the lens groups are varied at the time of focus adjustment areindicated as “variable DA”, “variable DB”, “variable DC”, “variable DD”,and “variable DE” in TABLE 10, and as illustrated in next TABLE 10, thesurface distances DA to DE are varied with respect to the diagonal sizes60, 80, and 100 inches of the projection image.

TABLE 10 VARIABLE DISTANCE FOCUSING SHORT LONG DISTANCE STANDARDDISTANCE SCREEN SIZE 60 INCHES 80 INCHES 100 INCHES VARIABLE DA 2.003.03 3.54 VARIABLE DB 4.81 4.48 4.31 VARIABLE DC 23.02 18.46 16.08VARIABLE DD 49.70 53.56 55.59 VARIABLE DE 297.04 385.42 473.41

Further, the shape of the free-form surface is specified by theabove-described expression (6), providing an inverse number of paraxialcurvature radius (paraxial curvature) C, a height from an optical axisH, a conic constant K, and free-form surface coefficients listed in nextTABLE 11 while defining X as an amount of the free-form surface in theoptical axis direction.

TABLE 11 FREE-FORM SURFACE COEFFICIENTS 33TH SURFACE K 0 C4 1.0582E−02C6 −8.2531E−04  C8 9.9460E−05 C10 −2.2150E−04  C11 −7.4734E−07  C137.7163E−06 C15 −3.5768E−07  C17 −2.8343E−08  C19 1.8056E−07 C213.8225E−08 C22 1.1049E−10 C26 1.0935E−09 C28 4.2954E−10 C30 −2.2417E−12 C32 −5.5901E−11  C34 −1.3183E−11  C36 −1.7253E−13  C37 −1.6625E−14  C393.3160E−15 C41 −5.9419E−13  C43 −1.2863E−13  C45 −1.7223E−14  C473.3385E−16 C49 1.8374E−15 C51 −1.5395E−15  C53 8.8023E−16 C55 6.2272E−17C56 1.5129E−18 C58 7.2133E−18 C60 1.7912E−17 C64 1.0211E−17 C661.1251E−18

Note that the projection distance and TR take values listed in nextTABLE 12 in accordance with the short distance side, standard, and longdistance side. Here, TR is expressed as:

[a distance to the screen from an intersection between the free-formsurface concave mirror 13 and the axis A]/[a lateral width of thescreen]

TABLE 12 PROJECTION DISTANCE AND TR SHORT LONG DISTANCE STANDARDDISTANCE 60 INCHES 80 INCHES 100 INCHES PROJECTION 299.67 388.02 476.00DISTANCE TR 0.226 0.219 0.215

Hereinafter, specific values of a DMD used as an image forming unit LVof the second example and others are shown.

DMD size

Dot size: 7.56 μm)

Length in lateral direction: 14.5152 mm

Length in vertical direction: 8.1648 mm

Optical axis to center of device: 5.30 mm

BF/Y: 3.45

Positional coordinates of the folding mirror 12 and free-form surfaceconcave mirror 13 from an apex in a focused state in which theprojection image of the lens positioned closest to a reflection surfaceside is maximized are shown in next TABLE 13. As for rotation, an anglemade by a surface normal and the optical axis is indicated.

TABLE 13 Y-AXIS Z-AXIS α 32ND SURFACE 0.00 55.59 −45.00 33TH SURFACE82.93 77.48 −102.80

Spot diagrams corresponding to respective field angles illustrated inFIG. 4 are illustrated in FIGS. 10 to 12. The respective spot diagramsrepresent imaging characteristics (mm) on the screen with respect towavelengths 625 nm (red), 550 nm (green), and 425 nm (blue). It is clearthat good imaging is performed.

That is, in the projection device according to the second example, thespot diagrams on the screen corresponding to the respective field angles(evaluation points) illustrated in FIG. 4 are illustrated in FIG. 10 inthe case of 100 inches, in FIG. 11 in the case of 80 inches, and in FIG.12 in the case of 60 inches, respectively.

As can be seen in FIGS. 10 to 12, it is clear that good imaging isperformed.

Focal lengths in the entire system and the first lens group in the caseof a room temperature (20 degrees) and the case of 40 degrees where thetemperature is increased by 20 more degrees are shown in next TABLE 14.

TABLE 14 20 DEGREES 40 DEGREES ENTIRE SYSTEM 20.19 20.20 FIRST LENSGROUP 41.97 41.99

This shows that change of the focal lengths at the time of temperaturechange is suppressed.

Note that values corresponding to the conditional expressions (1) to (4)are as shown below and satisfy the respective conditional expressions(1) to (4) in the case of the second example:

-   -   Conditional expression (1): dnT=−4.4    -   Conditional expression (2): vd=74.7031    -   Conditional expression (3): TR=0.215 to 0.226    -   Conditional expression (4): BF/Y=3.45

According to the projection device specified by the specific exemplaryvalues, the image projection device having an ultra-short projectiondistance, formed in a compact size, and having high performance andexcellent temperature characteristics can be achieved by designating theappropriate glass material for each of the positive lens and thenegative lens inside the fixed lens group. While the preferableembodiments of the present invention have been described in the abovefirst and second examples of the first embodiment, the present inventionis not limited to the content thereof.

Especially, the specific shapes and values of the respective componentsexemplified in the first and second examples of the first embodiment aremerely examples to implement the present invention, and it should not beunderstood that a technical scope of the present invention is limited bythese examples.

Referring now to FIGS. 13 to 32, a projection device and a projectionsystem including the projection device will be described according to asecond embodiment of the present invention.

Before describing specific examples, concept of the second embodiment ofthe present invention will be described.

The present invention is a projection device to magnify and project, ona screen, an image displayed at an image display element. The projectiondevice includes a dioptric system and a reflection optical system havinga reflection optical element including at least one magnification. Thedioptric system includes at least one cemented lens, and the cementedlens includes at least one in each of a positive lens P1 and a negativelens N1 satisfying following conditional expressions (7), (8), (9), and(10):

4<dnTP  (7)

0.61<θgFP  (8)

3<dnTN  (9)

0.59<θgFN  (10)

where

a temperature coefficient of a relative refractive index in an e linewithin a range of 40 to 60 degrees of the positive lens P1 is dnTP,

a partial dispersion ratio in a g line and an F line of the positivelens P1 is θgFP,

a temperature coefficient of a relative refractive index in the e linewithin a range of 40 to 60 degrees of the negative N1 is dnTN,

a partial dispersion ratio of the negative lens N1 is θgFN,

and a partial dispersion ratio is θgf, the partial dispersion ratio θgfbeing expressed by an expression: θgf=(Ng−NF)/(NF−NC), where

a refractive index relative to the g line is Ng,

a refractive index relative to the F line is NF, and

a refractive index relative to a C line is NC.

When glass material of the positive lens P1 and the negative lens N1satisfies the conditional expressions (7) and (9), not only change of afocal length caused by temperature increase can be corrected by the twolenses but also particularly change of imaging surface curvature can behighly corrected. As a result, good resolution can be obtained in everydetail in the ultra-short throw projector despite occurrence oftemperature increase.

Further, temperature compensation can be performed by satisfying theconditional expressions (7) and (9), but this is not sufficient foraberration correction, especially, chromatic aberration correction. Bothoptical performance and temperature characteristics can be achieved wellonly after the conditional expressions (8) and (10) are satisfied at thesame time. More preferably, following conditional expressions (7′) and(9′) are satisfied as well:

4.8<dnTP  (7′)

3.5<dnTN  (9′).

More preferably, the cemented lens is disposed more on a magnificationside than an aperture stop. By thus disposing the cemented lens,aberration correction can be effectively performed. Further, theaperture stop herein indicates a place where thickness of a luminousflux passing the dioptric system from an entire area of the imagedisplay element (entire luminous flux) becomes thinnest.

More preferably, the cemented lens is included in a lens group includingthe aperture stop. The lens group including the aperture stop is thelens group where the temperature tends to increase because the light isconcentrated, and a projection optical system having good temperaturecharacteristics can be achieved by disposing the cemented lens in thislens group.

More preferably, the cemented lens is included in a lens group on a sideclosest to the image display element. The projection optical systemhaving the good temperature characteristics can be achieved by disposingthe cemented lens in the lens group closest to the image displayelement.

More preferably, the cemented lens is included in a lens group which isnot moved at the time of focusing. The reason is that the goodtemperature characteristics can be achieved in respective image sizes.

More specifically, when an axis shared by a plurality of axisymmetriclenses of the dioptric system is defined as an optical axis A, at leastone resin lens satisfying following conditional expressions (11) and(12) is included in a lens group which is moved at the time of focusing:

|P40d(h)−P20d(h)|×FP<0.02  (11)

|h|<0.85×D  (12)

where

a height from the optical axis A is h,

a distance between the optical axis A and a point where a distance fromthe optical axis A becomes largest out of intersections between areduction-side lens surface and a beam is D,

a paraxial focal length in a line d of the resin lens is FP,

a magnification when a temperature at the height h from the optical axisA is 40 degrees is P40 d(h), and

a magnification when the temperature at the height h from the opticalaxis A is 20 degrees is P20 d(h).

An imaging surface particularly in a periphery of a screen can be highlycorrected by using the resin lens including an aspheric surface or afree-form surface for a group that is moved at the time of focus.However, in the case of intending to improve an effect of imagingsurface correction, the imaging surface is largely moved by change ofthe magnification at the time of temperature increase. The conditionalexpression (11) represents a magnification difference at the certainlens height h between the case of having the room temperature and thecase where the temperature is increased by 20 more degrees from the roomtemperature. The conditional expression (12) represents a range of theheight h. By controlling the magnification difference in the conditionalexpression (11) to be an upper limit or less in a lens diameter range ofthe conditional expression (12), thereby achieving to minimize tilt ofthe imaging surface at the time of temperature increase. Also, theimaging surface in the periphery of the screen can be highly correctedeven at the time of temperature increase by further satisfying theconditional expressions (7), (8), (9), (10), (11), and (12) at the sametime.

More preferably, the resin lens is included in a lens group that ismoved at the time of focusing. With this arrangement, image surfacecurvature caused by temperature change can be effectively prevented.

More preferably, the reflection optical element is a concave mirror andincludes a free-form surface. The image surface curvature can beeffectively corrected by using the free-form surface.

More preferably, the conditional expression (4) is satisfied when anaxis shared by the plurality of axisymmetric lenses of the dioptricsystem is set as an optical axis:

BF/Y<4.0  (4)

where

BF denotes a distance from an intersection between a surface includingthe image display element and the optical axis to a vertex of a displayelement side surface of a lens closest to the display element, and

a maximum value of a distance between the optical axis and an endportion of an image forming unit is Y.

The projection optical system can be downsized by satisfying theconditional expression (4). Further, more preferably, a followingconditional expression (4′) is satisfied as well:

BF/Y<3.5  (4′).

More preferably, the projection optical system is a non-telecentricoptical system. Adoption of the non-telecentric optical system isadvantageous in downsizing.

More preferably, the conditional expression (3) is satisfied as well:

TR<0.30  (3)

where

a distance to a screen from an intersection between the concave mirrorand the optical axis A/lateral width of a screen is TR.

The projection device having an extremely short projection distance canbe achieved by satisfying the conditional expression (3). Morepreferably, a conditional expression (3′) is satisfied as well:

TR<0.27  (3′).

As described above, with the above-described configuration, theprojection optical system can have the extremely short projectiondistance and higher luminance, and a projection image display deviceformed in a compact size and having high performance and excellenttemperature characteristics can be provided.

Second Embodiment First Example

Next, a configuration of a projection optical system of a projectiondevice according to the above-described embodiment of the presentinvention will be described in detail.

FIG. 13 is a cross-sectional view illustrating the configuration of theprojection device together with an optical path according to a firstexample of the second embodiment of the present invention.

FIG. 14 is an explanatory diagram illustrating a positional relationbetween an optical axis and a center of an image forming unit in whichan image is formed, when the image forming unit is shifted inY-direction by a predetermined amount relative to the optical axis.

FIG. 15 (FIG. 15A and FIG. 15B) is a cross-sectional view illustratingmoving positions of a focusing lens for each projection size of theprojection optical system used in the projection device according to thefirst example of the second embodiment of the present invention, andFIG. 15A illustrates a case where the projection size is a long distanceside (100 inches), and FIG. 15B illustrates a case where the projectionsize is a short distance side (80 inches).

In FIG. 13, a reference sign LV indicates the image forming unit. Theimage forming unit LV is, more specifically, a light valve such as a“Digital Micro-mirror Device (abbreviated as DMD)”, a “transmissiveliquid crystal panel”, and a “reflective liquid crystal panel”, and aportion indicated by the reference sign LV is a “portion where an imageto be projected is formed”. In the case where the image forming unit LVdoes not have a function to emit light by itself like the DMD, imageinformation formed at the image forming unit LV is illuminated byillumination light from an illumination optical system LS. For theillumination optical system LS, a system having a function toeffectively illuminate the image forming unit LV is preferable.

Further, for example, a rod integrator and a fly-eye integrator can beused in order to uniform illumination. Additionally, for a light sourceof the illumination, a white light source such as a super-high pressuremercury lamp, a xenon lamp, a halogen lamp, and an LED can be used.Further, a monochromatic light source such as a monochromatic LED and aLaser Diode (LD) can be also used. A known technology is adopted as theillumination optical system. Therefore, providing a specific example isomitted here.

According to the present embodiment, the DMD is assumed as the imageforming unit LV. Further, the present embodiment has a precondition that“the image forming unit does not have a function to emit light” byitself, but an image forming unit including “a self-light emittingsystem having a function to cause a generated image to emit light” canbe also used.

A parallel plate F disposed in the vicinity of the image forming unit LVis assumed to be a cover glass (seal glass) of the image forming unitLV. A reference sign H represents an outer surface of the projectiondevice, and a reference sign S represents a stop (aperture stop).Further, a reference sign SC in FIG. 13 represents a screen.

FIG. 13 illustrates an optical path diagram in the case of 80 inches inwhich a front lens element is most protruded. As illustrated in FIG. 13,an axis shared by a plurality of axisymmetric lenses is defined as anoptical axis A, a direction parallel to the optical axis A is defined asZ-axis direction, an axis vertical to the optical axis A within asurface including a beam emitted from a center of the image displayelement and passing a center of the stop S is defined as a Y-axis, andan axis vertical to the optical axis A and Y-axis is defined as anX-axis. In FIG. 13, a clockwise rotary direction is defined as +adirection.

A luminous flux having intensity two-dimensionally modulated by theimage information at the DMD is to be a projected luminous flux as anobject light. The projected luminous flux from the image forming unit LVpasses a dioptric system 11, a folding mirror 12, and a free-formsurface concave mirror 13, and becomes an imaging luminous flux. Inother words, an image formed on the DMD (image forming unit LV) ismagnified and projected on the screen SC by the projection opticalsystem, and becomes a projection image. Here, a surface on which theimage is formed is defined as an image forming surface. Respectiveoptical elements in the dioptric system 11 share an optical axisindividually, and the image forming unit LV is shifted in theY-direction relative to the optical axis A as illustrated in FIG. 14.

According to the first example of the second embodiment, the system isformed by using the dioptric system 11, folding mirror 12, and onefree-form surface concave mirror 13. The number of mirrors may beincreased, but this is not so preferable because the configuration maybecome complex and upsized, and cost increase may be caused as well.

Heat generation by absorbing heat and light from a power source and alamp is increased in the illumination optical system LS along withenhancement of higher luminance. Particularly, in the projector usingthe non-telecentric optical system, a light absorption amount to a lensbarrel is largely increased by shortening back focus for downsizing.Therefore, a lens group closest to an image display side has thetemperature easily increased, and temperature compensation is neededinside the lens group.

Considering above, in the first example of the second embodiment, changeof a focal length and expansion of a mechanical holder caused by heatare balanced by using glass material satisfying conditional expressions(7), (8), (9), and (10) (for example, S-NBH56 having nd: 1.85478, vd:24.799, dnTP: 5.1, and θgFP: 0.6122 of OHARA INC., and TAFD25 having nd:1.90366, vd: 31.315 dnTN: 3.6, θgFN: 0.5947 of HOYA CORPORATION) foreach of a positive lens P1 and a negative lens N1 of a cemented lensdisposed closer to the magnification side than the stop S. Further, inaddition to the above, an aspheric surface lens is adopted for apositive lens closest to an image display element side, therebyachieving to highly adjust temperature change at the image surfacecurvature.

Moreover, by appropriately disposing a cooling mechanism, temperaturechange can be suppressed for the lens group which has the asphericsurface lens and is moved at the time of focus, and temperature changeat the image surface curvature can be suppressed.

The light having passed the dioptric system 11 forms, as a space image,an intermediate image on a side closer to the image forming unit LV thanthe folding mirror 12. The intermediate image is conjugate to the imageinformation formed on the image forming unit LV. The intermediate imageis not necessarily imaged as a planar image, and formed as a curvedimage in both the first embodiment and other embodiments. Theintermediate image is magnified and projected by the free-form surfaceconcave mirror 13 disposed closest to the magnification side, andscreened on the screen SC. The intermediate image includes image surfacecurvature and distortion, but the curvature and distortion can becorrected by using the free-form surface concave mirror 13.

Therefore, a lens system has a reduced burden to perform aberrationcorrection, thereby increasing freedom of design and having an advantagein downsizing, for example. Further, the free-form surface referredherein is an anamorphic surface in which X-direction curvaturecorresponding to an X-direction position in an optional Y-directionposition is not constant, and Y-direction curvature corresponding to aY-direction position in an optional X-direction position is notconstant.

Preferably, a dust-proof glass 14 is disposed between the free-formsurface concave mirror 13 and the screen SC. According to the presentfirst embodiment, a flat plate glass is used as the dust-proof glass 14,but the glass may also have curvature, or may be an optical elementhaving a magnification such as a lens. Further, the duct-proof glass isdisposed tilted to the optical axis A instead of being vertical, but thetilting angle is optional and may be vertical to the optical axis A.

Next, the first example of the second embodiment of the presentinvention will be described in detail with reference to FIG. 15.

The reference signs in the first example and a later-described secondexample are defined as follows.

f: focal length in entire system

NA: numerical aperture

ω: half field angle (deg.)

R: curvature radius (paraxial curvature radius on the aspheric surface)

D: surface distance

Nd: refractive index

vd: Abbe number

K: conic constant of aspheric surface

Ai: i^(th) aspheric surface coefficient

Cj: free-form surface coefficient

A shape of the aspheric surface is expressed by a following knownexpression (13) by setting X as an amount of the aspheric surface in theoptical axis direction, defining that:

C: an inverse of paraxial curvature radius (paraxial curvature);

H: a height from optical axis; and

K: a conic constant, and

using the above-mentioned aspheric surface coefficient of each degree.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 13} \right\rbrack & \; \\{X = {\frac{C \cdot H^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right) \cdot C^{2} \cdot H^{2}}}} + {\sum\limits_{i = 1}{{Ai} \cdot H^{i}}}}} & \;\end{matrix}$

The shape is specified by providing the paraxial curvature radius, conicconstant, and aspheric surface coefficient.

Further, a shape of the free-form surface is specified by a followingknown expression (14) by setting X as an amount of the free-form surfacein the optical axis direction, defining that:

C: an inverse number of paraxial curvature radius (paraxial curvature);

H: a height from the optical axis; and

K: a conic constant, and

using the above-mentioned free-form surface coefficient.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 14} \right\rbrack & \; \\{X = {\frac{C \cdot H^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right) \cdot C^{2} \cdot H^{2}}}} + {\sum\limits_{j = 1}{{{Cj} \cdot x^{m}}y^{n}}}}} & \;\end{matrix}$

However, there is a following condition.

$j = {\frac{\left( {m + n} \right)^{2} + m + {3n}}{2} + 1}$

The shape of the free-form surface is specified by providing theparaxial curvature radius, conic coefficient, and free-form surfacecoefficient.

As illustrated in FIG. 13, the Z-axis is an axis in a normal directionof the image forming unit and also an axis parallel to the optical axisA which is the axis shared by axisymmetric lenses. Among the axes withinthe surface including the beam emitted from the center of the imagedisplay element and passing the center of the stop S, an axis verticalto the axis A is defined as the Y-axis, and an axis vertical to theoptical axis A and the Y-axis is defined as the X-axis. In FIG. 13, theclockwise rotary direction is defined as +α direction.

Further, a curvature radius p at a distance h from the optical axis onthe aspheric surface is calculated by a following expression. Theexpression of the aspheric surface f(h) is differentiated by h, and thecurvature radius is acquired by using the following expression.

[Expression]${{f^{\prime}h} = \frac{{f(h)}}{h}},{{f^{''}h} = \frac{^{2}{f(h)}}{h^{2}}},{p = \frac{f^{''}h}{\left\{ {1 + \left( {f^{\prime}h} \right)^{2}} \right\}^{3/2}}}$

In FIG. 15, a lens structure of the dioptric system and a focusing stateaccording to the first example of the second embodiment of the presentinvention are illustrated. In this dioptric system, a first lens groupG1 having positive refractive power, a second lens group G2 havingpositive refractive power, a third lens group G3 having negativerefractive power, and a fourth lens group G4 having positive refractivepower are sequentially arranged in a direction from the image formingunit side to the magnification side. In performing focusing in responseto change of the projection distance, the positive second lens group G2and the negative third lens group G3 are moved to the image forming unitside, and the positive fourth lens group G4 is moved to themagnification side at the time of focusing from the long distance side(100 inches) to the short distance side (80 inches).

The first lens group G1 includes, sequentially from the image formingunit LV side:

a first lens L1 formed of a double-sided aspheric biconvex lens in whicha convex surface having larger curvature than the magnification side isoriented to the image forming unit side;

a second lens L2 formed of a negative meniscus lens in which a convexsurface is oriented to the image forming unit side,

a cemented lens including a third lens L3 formed of a negative meniscuslens in which a convex surface is oriented to the image forming unitside, and a fourth lens L4 formed of a positive meniscus lens in which aconvex surface is oriented to the image forming unit;

the stop S;

a fifth lens L5 formed of a negative meniscus lens in which a convexsurface is oriented to the magnification side;

a sixth lens L6 formed of a double-sided aspheric biconvex lens in whicha convex surface having larger curvature than the image forming unitside is oriented to the magnification side;

a seventh lens L7 formed of a negative meniscus lens in which a convexsurface is oriented to the image forming unit side;

a cemented lens including an eighth lens L8 formed of a biconvex lens inwhich a convex surface having larger curvature than the image formingunit side is oriented to the magnification side, and a ninth lens L9formed of a biconcave lens in which a concave surface having largercurvature than the magnification side is oriented to the image formingunit side; and

a tenth lens L10 formed of a biconvex lens in which a convex surfacehaving larger curvature than the magnification side is oriented to theimage forming unit side.

The second lens group G2 includes an eleventh lens L11 formed of apositive meniscus lens in which a convex surface is oriented to theimage forming unit side.

The third lens group G3 includes a twelfth lens L12 formed of abiconcave lens in which a concave surface having curvature larger thanthe magnification side is oriented to the image forming unit side, and athirteenth lens L13 formed of a double-sided aspheric negative meniscuslens PL made of resin in which a convex surface is oriented to the imageforming unit side.

The fourth lens group G4 includes a fourteenth lens L14 formed of adouble-sided aspheric surface positive meniscus lens in which a convexsurface is oriented to the magnification side.

The dioptric system is formed of the above lens groups, and the foldingmirror 12 (surface 30) which is a flat surface mirror and the free-formsurface concave mirror 13 (surface 31) are disposed on the magnificationside thereof.

Note that the eighth lens L8 is referred to as the positive lens P1, andthe ninth lens L9 is referred to as the negative lens N1.

In the following, lens data is listed in TABLE 15. In the TABLE 15, asurface number attached with * is the aspheric surface, and a surfacenumber attached with ** is the free-form surface.

TABLE 15 NUMERICAL APERTURE: 0.200 EFFECTIVE R D Nd vd GLASS MATERIALDIAMETER D  1 ∞ 1.00  2 ∞ 1.00 1.51633 64.142 S-BXL7 OHARA 8.25  3 ∞29.00  8  4* 16.079 4.80 1.49700 81.5459 S-FPL51 OHARA 7.5  5* −89.7881.67 7.1  6 206.572 2.30 1.74000 28.2960 S-TIH3 OHARA 7.5  7 32.959 1.097.1  8 26.761 2.42 1.90366 31.3150 TAFD25 HOYA 7.1  9 13.739 2.691.53775 74.7031 S-FPM3 OHARA 6.5 10 61.626 0.83 6.4 STOP ∞ 3.37 6.4 11−28.002 1.00 1.53775 74.7031 S-FPM3 OHARA 6.8 12 −60.555 0.60 7.0 13*24.520 4.11 1.58913 61.1526 L-BAL35 OHARA 7.4 14* −21.460 1.55 7.2 1566.842 2.47 1.80400 46.5834 S-LAH65V OHARA 8.0 16 21.739 1.07 7.9 1742.163 5.64 1.85478 24.7990 S-NBH56 OHARA 8.0 18 −13.240 0.90 1.9036631.3150 TAFD36 HOYA 8.2 19 27.595 12.88  6.7 20 46.438 7.52 1.6030065.4436 S-PHM53 OHARA 17.6 21 −84.414 VARIABLE DA 18.0 22 36.209 5.201.75700 47.8232 S-LAM54 OHARA 19.3 23 64.941 VARIABLE DB 18.8 24 −45.9962.00 1.74950 35.3325 S-NBH51 OHARA 18.4 25 86.417 3.77 19.3 26* 45.1992.00 1.53046 55.8000 RESIN 19.8 27* 24.072 VARIABLE DC 21.0 28* −39.5154.80 1.53046 55.8000 RESIN 23.9 29* −33.469 VARIABLE DD 24.9 30 ∞−86.27  REFLECTION SURFACE 31** ∞ VARIABLE DE REFLECTION SURFACE

More specifically, in TABLE 15, a fourth surface, a fifth surface, athirteenth surface, a fourteenth surface, a twenty-sixth surface, atwenty-seventh surface, a twenty-eighth surface, and a twenty-ninthsurface attached with “*” have respective optical surfaces which areaspheric surfaces, and parameters of the respective aspheric surfaces inthe expression (13) are as shown in next TABLE 16.

Note that “En” is “exponent of 10”, that is, “×10^(n)” in the asphericsurface coefficient. For example, “E-05” represents “×10⁻⁵”.

TABLE 16 ASPHERIC SURFACE COEFFICIENTS K A4 A6 A8 A10 A12 A14 A16 4TH0.5377 −2.3967E−05 −2.9939E−08  SURFACE 5TH −129.0056  2.3918E−051.7125E−07 3.5858E−10 SURFACE 13TH −0.0703 −1.1700E−05 SURFACE 14TH−0.7746  1.8915E−05 6.7969E−09 SURFACE 26TH −12.7046 −3.8470E−05−1.4633E−08  5.0093E−10 −1.5116E−12 1.2508E−15  1.33153E−18 −1.90159E−21SURFACE 27TH −1.8124 −7.6226E−05 1.5444E−07 −1.5176E−10  −9.0626E−142.4797E−16 −5.24635E−20 SURFACE 28TH −0.6508 −4.6949E−05 1.0727E−07−4.6534E−10   1.7785E−12 −2.7318E−15   1.44741E−18 SURFACE 29TH −1.4422−3.5579E−05 3.0092E−08 3.4901E−11 −6.3482E−13 2.7655E−15 −4.20592E−18 2.14222E−21 SURFACE

DA, DB, DC, DD, and DE in TABLE 15 represent variable distances.

Among the distances, the variable distance DA is a distance between thefirst lens group G1 and the second lens group G2, namely, the variabledistance between surface 21 and a surface 22. The variable distance DBis a distance between the second lens group G2 and the third group G3,namely, the variable distance between a surface 23 and a surface 24. Thevariable distance DC is a distance between the third lens group G3 and afourth lens group G4, namely, the variable distance between a surface 27and a surface 28.

The variable distance DD is a distance between the fourth lens group G4and the folding mirror 12, and DE is the variable distance between thefree-form surface concave mirror 13 and the screen SC.

Thus, in the projection optical system, the second lens group G2 and thethird lens group G3 are moved to the image forming unit side and thefourth lens group G4 is moved to the magnification side in FIG. 15 atthe time of focusing from the long distance side to the short distanceside to perform focusing in response to the change of the projectiondistance. Thus, by changing a magnifying ratio, focus adjustment isperformed in a range from 80 inches to 100 inches in a diagonal size ofthe projection image in accordance with a projection size.

At the time of focus adjustment, surface distances DA, DB, DC, DD, DE inwhich the distances between the lens groups are varied are indicated as“variable DA”, “variable DB”, “variable DC”, “variable DD”, and“variable DE” in TABLE 15, and as illustrated in next TABLE 17, thesurface distances DA to DE are varied with respect t the diagonal sizes100, 80, 60 inches of the projection image.

TABLE 17 VARIABLE DISTANCE FOCUSING SHORT LONG DISTANCE STANDARDDISTANCE SCREEN SIZE 60 INCHES 80 INCHES 100 INCHES VARIABLE DA 2.003.63 4.52 VARIABLE DB 10.80 10.22 9.90 VARIABLE DC 20.27 17.79 16.33VARIABLE DD 53.01 54.44 55.33 VARIABLE DE 344.24 445.94 547.55

Further, the shape of the free-form surface is specified by theabove-described expression (14), providing an inverse number of paraxialcurvature radius (paraxial curvature) C, a height from optical axis H, aconic constant K, and free-form surface coefficients listed in nextTABLE 18 while defining X as an amount of the free-form surface in theoptical axis direction.

TABLE 18 FREE-FORM SURFACE COEFFICIENTS 31TH SURFACE K 0 C4 9.6570E−03C6 2.9613E−03 C8 8.1331E−05 C10 −1.0990E−04  C11 −6.4957E−07  C136.3007E−06 C15 9.5851E−07 C17 −3.4964E−08  C19 1.4710E−07 C21 4.2619E−08C22 8.7305E−11 C26 1.0071E−09 C28 3.9365E−10 C30 6.5275E−13 C32−5.3383E−11  C34 −8.8261E−12  C36 −1.5344E−13  C37 −8.8747E−15  C397.0181E−14 C41 −6.1523E−13  C43 −1.1310E−13  C45 −8.4549E−15  C471.6404E−16 C49 1.9388E−15 C51 −2.7866E−15  C53 3.8760E−16 C55 1.5794E−16C56 7.4048E−19 C58 3.3980E−18 C60 1.4570E−17 C64 6.7592E−18 C661.4736E−18

Note that the projection distance and TR take values listed in nextTABLE 19 in accordance with the short distance, standard, and longdistance. Here note that TR is expressed as:

[distance to screen from intersection between free-form surface concavemirror 13 and optical axis A]/[lateral width of screen]

TABLE 19 PROJECTION DISTANCE AND TR SHORT LONG DISTANCE STANDARDDISTANCE 60 INCHES 80 INCHES 100 INCHES PROJECTION 347.24 448.94 550.55DISTANCE TR 0.261 0.253 0.249

In the following, specific values of the DMD used as the image formingunit LV and others according to the first example of the secondembodiment are shown.

DMD size

Dot size: 7.56 μm

Length in lateral direction: 14.5152 mm

Length in vertical direction: 8.1648 mm

Optical axis to center of device: 5.30 mm

BF/Y: 3.45

Positional coordinates of the folding mirror 12 and free-form surfaceconcave mirror 13 from an apex in a focused state are shown in nextTABLE 20. In the focused state, the projection image of the lenspositioned closest to a reflection surface side is maximized. Meanwhile,as for rotation, an angle formed between a surface normal and theoptical axis is indicated.

TABLE 20 Y-AXIS Z-AXIS α 30TH SURFACE 0.00 55.59 −45.00 31ST SURFACE82.93 77.48 −102.80

Spot diagrams corresponding to respective field angles illustrated inFIG. 17 are illustrated in FIG. 18 (in the case of 100 inches), FIG. 19(in the case of 80 inches), and FIG. 20 (in the case of 60 inches). Therespective spot diagrams represent imaging characteristics (mm) on thescreen with respect to wavelengths 625 nm (red), 550 nm (green), and 425nm (blue). It is clear that good imaging is performed.

The paraxial focal lengths in the entire system and the first lens groupare shown in next TABLE 21 in the case of 100 inches when thetemperature is a room temperature (20 degrees) and when the temperatureis increased by 20 more degrees.

TABLE 21 20 DEGREES 40 DEGREES ENTIRE SYSTEM 20.86 20.87 FIRST LENSGROUP 35.48 35.49

This shows that change of the focal length is suppressed at the time oftemperature change.

Further, FIGS. 21 to 23 illustrate spot diagrams in the respective imagesizes (100 inches, 80 inches, 60 inches) when the temperature isincreased by 20 more degrees from the room temperature (20 degrees).

FIGS. 21 to 23 also show good imaging performance even at the time oftemperature increase.

Note that the values corresponding to the conditional expressions (3),(4), and (7) to (12) are as shown below and satisfy the respectiveconditional expressions (3), (4), and (7) to (12) in the case of thepresent example:

-   -   Conditional expression (7): dnTP=5.1    -   Conditional expression (8): θgFP=0.6122    -   Conditional expression (9): dnTN=3.6    -   Conditional expression (10): θgFN=0.5947    -   Conditional expression (11): |P40d(h)−P20d(h)|×FP=0.02 or less    -   Conditional expression (12): 0.85>D=16.745    -   Conditional expression (3): TR=0.261 (in the case of short        distance 60 inches)    -   : TR=0.254 (in the case of standard distance 80 inches)    -   : TR=0.249 (in the case of long distance 100 inches)    -   Conditional expression (4): BF/Y=3.45.

Further, as illustrated in FIG. 16, the conditional expression (12) issatisfied within a range of conditional expression (11).

Second Example

FIG. 24 is a cross-sectional view illustrating a configuration of aprojection device together with an optical path according to a secondexample of the second embodiment of the present invention.

FIG. 25 (FIGS. 25A and 25B) is a cross-sectional view illustratingmoving positions of a focusing lens for each projection size of theprojection optical system used in the projection device according to thesecond example of the second embodiment of the present invention, andFIG. 25A illustrates a case where the projection size is a long distanceside (100 inches), and FIG. 25B illustrates a case where the projectionsize is a short distance side (80 inches).

In FIG. 24, a reference sign LV indicates an image forming unit. Theimage forming unit LV is, more specifically, a light valve such as a“Digital Micro-mirror Device (abbreviated as DMD)”, a “transmissiveliquid crystal panel”, and a “reflective liquid crystal panel”, and aportion indicated by the reference sign LV is a “portion where an imageto be projected is formed”. In the case where the image forming unit LVdoes not have a function to emit light by itself like the DMD, imageinformation formed at the image forming unit LV is illuminated byillumination light from an illumination optical system LS. For theillumination optical system LS, a system having a function toeffectively illuminate the image forming unit LV is preferable. Further,for example, a rod integrator and a fly-eye integrator can be used inorder to uniform illumination. Additionally, for a light source of theillumination, a white light source such as a super-high pressure mercurylamp, a xenon lamp, a halogen lamp, and an LED can be used. Further, amonochromatic light source such as a monochromatic LED and a Laser Diode(LD) can be also used. A known technology is adopted as the illuminationoptical system. Therefore, providing a specific example is omitted here.

According to the present embodiment, a DMD is assumed as the imageforming unit LV. Further, the present embodiment has a precondition that“the image forming unit does not have a function to emit light” byitself, but an image forming unit including “a self-light emittingsystem having a function to cause a generated image to emit light” canbe also used.

A parallel plate F disposed in the vicinity of the image forming unit LVis assumed to be a cover glass (seal glass) of the image forming unitLV. A reference sign H represents an external portion of the projectiondevice, and a reference sign S represents a stop (aperture stop).Further, a reference sign SC in FIG. 24 represents a screen.

FIG. 24 illustrates an optical path diagram in the case of 80 inches inwhich a front lens element is most protruded. As illustrated in FIG. 24,an axis shared by a plurality of axisymmetric lenses is defined as anoptical axis A, a direction parallel to the optical axis A is defined asZ-axis direction, an axis vertical to the optical axis A within asurface including a beam emitted from a center of the image displayelement and passing a center of the stop S is defined as a Y-axis, andan axis vertical to the optical axis A and Y-axis is defined as anX-axis. In FIG. 24, a clockwise rotary direction is defined as +adirection.

A luminous flux having intensity two-dimensionally modulated by theimage information at the DMD is to be a projected luminous flux as anobject light. The projected luminous flux from the image forming unit LVpasses a dioptric system 11, a folding mirror 12, and a free-formsurface concave mirror 13, and becomes an imaging luminous flux. Inother words, an image formed on the DMD (image forming unit LV) ismagnified and projected on the screen SC by the projection opticalsystem, and becomes a projection image.

Here, a surface on which the image is formed is defined as an imageforming surface. Respective optical elements in the dioptric system 11share an optical axis individually, and the image forming unit LV isshifted in the Y-direction relative to the optical axis A as illustratedin FIG. 14.

According to the second embodiment, the system is formed by using thedioptric system 11, folding mirror 12, and free-form surface concavemirror 13. The number of mirrors may be increased, but this is not sopreferable because the configuration may become complex and upsized, andcost increase may be caused as well.

Heat generation by absorbing heat and light from a power source and alamp is increased in the illumination optical system LS along withenhancement of higher luminance. Particularly, in a projector using anon-telecentric optical system, a light absorption amount to a lensbarrel is largely increased by shortening a back focal length fordownsizing. Therefore, a lens group closest to an image display side hastemperature easily increased, and temperature compensation is neededinside the lens group.

Considering above, in the second example of the second embodiment,change of a focal length and expansion of a mechanical holder caused byheat is balanced by using glass material satisfying conditionalexpressions (7), (8), (9), and (10) (for example, S-NBH56 having nd:1.85478, vd: 24.799, dnTP: 5.1, and θgFP: 0.6122 of OHARA INC., andTAFD25 having nd: 1.90366, vd: 31.315 dnTN: 3.6, θgFN: 0.5947 of HOYACORPORATION) for each of a positive lens P1 and a negative lens N1 of acemented lens disposed closer to the magnification side than the stop S.Further, in addition to the above, an aspheric surface lens is adoptedas a positive lens closest to an image display element side, therebyachieving to highly adjust temperature change at image surfacecurvature.

Moreover, by appropriately disposing a cooling mechanism, temperaturechange can be suppressed for the lens group which has the asphericsurface lens and is moved at the time of focus, and temperature changeat the image surface curvature can be suppressed.

The light having passed the dioptric system 11 forms, as a space image,an intermediate image on a side closer to the image forming unit LV thanthe folding mirror 12. The intermediate image is conjugate to the imageinformation formed on the image forming unit LV. The intermediate imageis not necessarily imaged as a planar image, and formed as a curvedimage in both the second embodiment and other embodiments. Theintermediate image is magnified and projected by the free-form surfaceconcave mirror 13 disposed closest to the magnification side, andscreened on the screen SC. The intermediate image includes image surfacecurvature and distortion, but the curvature and distortion can becorrected by using the free-form surface concave mirror 13.

Therefore, a lens system has a reduced burden to perform aberrationcorrection, thereby increasing freedom of design and having an advantagein downsizing, for example. Further, the free-form surface referredherein is an anamorphic surface in which X-direction curvaturecorresponding to an X-direction position in an optional Y-directionposition is not constant, and Y-direction curvature corresponding to aY-direction position in an optional X-direction position is notconstant.

Preferably, a dust-proof glass 14 is disposed between the free-formsurface concave mirror 13 and the screen SC. According to the secondembodiment, a flat plate glass is used for the dust-proof glass 14, butthe glass may also have curvature, or may be an optical element having amagnification such as a lens. Further, the duct-proof glass is disposedtilted to the optical axis A instead of being vertical, but the tiltingangle is optional and may be vertical to the optical axis A.

FIG. 24 illustrates a lens structure of the dioptric system and afocusing state according to the second example of the second embodimentof the present invention. In this dioptric system, a first lens group G1having positive refractive power, a second lens group G2 having positiverefractive power, a third lens group G3 having negative refractivepower, and a fourth lens group G4 having positive refractive power aresequentially arranged in a direction from the image forming unit side tothe magnification side. In performing focusing in response to change ofthe projection distance, the positive second lens group G2 and thenegative third lens group G3 are moved to the image forming unit side,and the positive fourth lens group G4 is moved to the magnification sideat the time of focusing from the long distance side (100 inches) to theshort distance side (80 inches).

The first lens group G1 includes, sequentially from the image formingunit LV side to the magnification side:

a first lens L1 formed of a double-sided aspheric biconvex lens in whicha convex surface having larger curvature than the magnification side isoriented to the image forming unit side;

a second lens L2 formed of a negative meniscus lens in which a convexsurface is oriented to the image forming unit side;

a cemented lens including a third lens L3 formed of a negative meniscuslens in which a convex surface is oriented to the image forming unitside, and a fourth lens L4 formed of a positive meniscus lens in which aconvex surface is oriented to the image forming unit;

the stop S;

a fifth lens L5 formed of a negative meniscus lens in which a convexsurface is oriented to the magnification side;

a sixth lens L6 formed of a double-sided aspheric biconvex lens in whicha convex surface having larger curvature than the image forming unitside is oriented to the magnification side;

a seventh lens L7 formed of a negative meniscus lens in which a convexsurface is oriented to the image forming unit side,

a cemented lens including an eighth lens L8 formed of a biconvex lens inwhich a convex surface having larger curvature than the image formingunit side is oriented to the magnification side, and a ninth lens L9formed of a biconcave lens in which a concave surface having largercurvature than the magnification side is oriented to the image formingunit side; and

a tenth lens L10 formed of a biconvex lens in which a convex surfacehaving larger curvature than the magnification side is oriented to theimage forming unit side.

The second lens group G2 includes an eleventh lens L11 formed of apositive meniscus lens in which a convex surface is oriented to theimage forming unit side.

The third lens group G3 includes a twelfth lens L12 formed of abiconcave lens in which a concave surface having curvature larger thanthe magnification side is oriented to the image forming unit side, and athirteenth lens L13 formed of a double-sided aspheric negative meniscuslens PL made of resin in which a convex surface is oriented to the imageforming unit side.

The fourth lens group G4 includes a fourteenth lens L14 formed of adouble-sided aspheric surface positive meniscus lens in which a convexsurface is oriented to the magnification side.

The dioptric system is formed of the above lens groups, and the foldingmirror 12 (surface 30) which is a flat surface mirror and the free-formsurface concave mirror 13 (surface 31) are disposed on the magnificationside thereof.

Note that the eighth lens L8 is referred to as the positive lens P1, andthe ninth lens L9 is referred to as the negative lens N1.

In the following, lens data is listed in TABLE 22. In the TABLE 22, asurface number attached with * is the aspheric surface, and a surfacenumber attached with ** is the free-form surface.

TABLE 22 NUMERICAL APERTURE: 0.200 EFFECTIVE R D Nd vd GLASS MATERIALDIAMETER D  1 ∞ 1.00  2 ∞ 1.00 1.51633 64.1420 S-BSL7 OHARA  3 ∞ 29.00  4* 16.048 4.80 1.49700 81.5459 S-FPL51 OHARA 8.25  5* −85.536 1.38 7.95 6 111.624 2.27 1.74000 28.2960 S-TIH3 OHARA 7.6  7 30.383 1.18 7.2  827.207 2.25 1.90366 31.3150 TAFD25 HOYA 7.1  9 13.755 3.12 1.5377574.7031 S-FPM3 OHARA 6.6 10 63.887 0.82 6.3 STOP ∞ 3.42 6.4 11 −26.2751.00 1.53775 74.7031 S-FPM3 OHARA 6.8 12 −56.602 0.60 7.1 13* 24.7664.21 1.58913 61.1526 L-BAL35 OHARA 7.6 14* −21.197 0.97 7.9 15 67.4432.66 1.80400 46.5834 S-LAH65V OHARA 8.0 16 21.739 1.10 8.0 17 43.0735.60 1.85478 24.7990 S-NBH56 OHARA 8.1 18 −13.494 0.90 1.90366 31.3150TAFD25 HOYA 8.2 19 27.364 12.92  8.7 20 47.244 7.60 1.60300 65.4436S-PHM53 OHARA 17.7 21 −79.679 VARIABLE DA 18.0 22 35.971 5.20 1.7570047.8232 S-LAM54 OHARA 19.4 23 64.935 VARIABLE DB 18.9 24 −46.113 2.001.74950 35.3325 S-NBH51 OHARA 18.4 25 85.115 3.69 19.3 26* 44.375 2.001.53046 55.8000 RESIN 19.8 27* 23.826 VARIABLE DC 21.0 28* −38.342 4.801.53046 55.8000 RESIN 23.8 29* −32.958 VARIABLE DD 24.8 30 ∞ −86.21 REFLECTION SURFACE 31** ∞ VARIABLE DE REFLECTION SURFACE

More specifically, in TABLE 22, a fourth surface, a fifth surface, athirteenth surface, a fourteenth surface, a twenty-sixth surface, atwenty-seventh surface, a twenty-eighth surface, and a twenty-ninthsurface attached with “*” have respective optical surfaces which areaspheric surfaces, and parameters of the respective aspheric surfaces inthe expression (13) are as shown in next TABLE 23.

Note that “En” is “exponent of 10”, that is, “×10^(n)” in the asphericsurface coefficient. For example, “E-05” represents “×10⁻⁵”.

TABLE 23 ASPHERIC SURFACE COEFFICIENTS K A4 A6 A8 A10 A12 A14 A16 4TH0.5845 −2.6875E−05 −4.6685E−08  SURFACE 5TH −102.0263  2.4705E−051.3539E−07 6.5230E−10 SURFACE 13TH −0.2242 −9.2289E−06 SURFACE 14TH−0.8331  1.9190E−05 5.8305E−09 SURFACE 26TH −12.1375 −3.7845E−05−1.9499E−08  5.5908E−10 −1.8734E−12 2.3480E−15 −2.27821E−19 −1.0808E−21SURFACE 27TH −1.7935 −7.5892E−05 1.5352E−07 −1.4244E−10  −1.4842E−133.8953E−16 −1.70315E−19 SURFACE 28TH −0.6513 −4.8232E−05 1.1572E−07−5.0227E−10   1.8861E−12 −2.8899E−15   1.53542E−18 SURFACE 29TH −1.4060−3.6199E−05 3.1817E−08 3.8156E−11 −6.7693E−13 2.9033E−15 −4.39848E−18 2.24094E−21 SURFACE

DA, DB, DC, DD, and DE in TABLE 22 represent variable distances.

Among the distances, the variable distance DA is a distance between thefirst lens group G1 and the second lens group G2, namely, the variabledistance between surface 21 and a surface 22. The variable distance DBis a distance between the second lens group G2 and the third group G3,namely, the variable distance between a surface 23 and a surface 24. Thevariable distance DC is a distance between the third lens group G3 and afourth lens group G4, namely, the variable distance between a surface 27and a surface 28.

The variable distance DD is a distance between the fourth lens group G4and the folding mirror 12, and DE is the variable distance between thefree-form surface concave mirror 13 and the screen SC.

Thus, in the projection optical system, the second lens group G2 and thethird lens group G3 are moved to the image forming unit side and thefourth lens group G4 is moved to the magnification side in FIG. 25 atthe time of focusing from the long distance side to the short distanceside to perform focusing in response to change of the projectiondistance. Thus, by changing a magnifying ratio, focus adjustment isperformed in a range from 80 inches to 100 inches in a diagonal size ofthe projection image in accordance with a projection size.

At the time of focus adjustment, surface distances DA, DB, DC, DD, DE inwhich the distances between the lens groups are varied are indicated as“variable DA”, “variable DB”, “variable DC”, “variable DD”, and“variable DE” in TABLE 22, and as illustrated in next TABLE 10, thesurface distances DA to DE are varied with respect to the diagonal sizes100, 80, 60 inches of the projection image.

TABLE 24 VARIABLE DISTANCE FOCUSING SHORT LONG DISTANCE STANDARDDISTANCE SCREEN SIZE 60 INCHES 80 INCHES 100 INCHES VARIABLE DA 2.003.63 4.54 VARIABLE DB 10.98 10.41 10.10 VARIABLE DC 20.43 18.06 16.64VARIABLE DD 52.85 54.16 54.98 VARIABLE DE 344.33 446.01 547.63

Further, a shape of the free-form surface is specified by theabove-described expression (14), providing an inverse number of paraxialcurvature radius (paraxial curvature) C, a height from optical axis H;and a conic constant K, and free-form surface coefficients listed innext TABLE 25, and defining X as an amount of the free-form surface inthe optical axis direction.

TABLE 25 FREE-FORM SURFACE COEFFICIENTS 31TH SURFACE K 0 C4 9.6874E−03C6 2.9464E−03 C8 8.1314E−05 C10 −1.1148E−04  C11 −6.5274E−07  C136.2819E−06 C15 9.3461E−07 C17 −3.4747E−08  C19 1.4733E−07 C21 4.2726E−08C22 8.8158E−11 C26 1.0110E−09 C28 3.9459E−10 C30 6.1707E−13 C32−5.3383E−11  C34 −8.8595E−12  C36 −1.7197E−13  C37 −9.1360E−15  C396.9171E−14 C41 −6.1544E−13  C43 −1.1323E−13  C45 −8.4025E−15  C471.6700E−16 C49 1.9423E−15 C51 −2.7748E−15  C53 3.9039E−16 C55 1.6027E−16C56 7.7700E−19 C58 3.4642E−18 C60 1.4661E−17 C64 6.7415E−18 C661.4757E−18

Note that a projection distance and TR take values listed in next TABLE26 in accordance with the short distance, standard, and long distance.Here note that TR is expressed as:

[distance to screen from intersection between free-form surface concavemirror 13 and optical axis A]/[lateral width of screen]

TABLE 26 PROJECTION DISTANCE AND TR SHORT LONG DISTANCE STANDARDDISTANCE 60 INCHES 80 INCHES 100 INCHES PROJECTION 347.33 449.01 550.63DISTANCE TR 0.261 0.254 0.249

In the following, specific values of the DMD used as the image formingunit LV and others according to the second example of the secondembodiment are shown.

DMD size

Dot size: 7.56 μm

Length in lateral direction: 14.5152 mm

Length in vertical direction: 8.1648 mm

Optical axis to center of device: 5.30 mm

BF/Y: 3.45

Positional coordinates of the folding mirror 12 and free-form surfaceconcave mirror 13 from an apex in a focused state are shown in nextTABLE 27. In the focused state, the projection image of the lensespositioned closest to a reflection surface side is maximized. Meanwhile,as for rotation, an angle formed between a surface normal and theoptical axis is indicated.

TABLE 27 Y-AXIS Z-AXIS α 30TH SURFACE 0.00 54.98 −45.00 31ST SURFACE86.21 74.51 −103.40

Spot diagrams corresponding to respective field angles illustrated inFIG. 17 are illustrated in FIG. 27 (in the case of 100 inches), FIG. 28(in the case of 80 inches), and FIG. 29 (in the case of 60 inches). Therespective spot diagrams represent imaging characteristics (mm) on thescreen with respect to wavelengths 625 nm (red), 550 nm (green), and 425nm (blue). It is clear that good imaging is performed.

The paraxial focal lengths in the entire system and the first lens groupare shown in next TABLE 28 in the case of 100 inches when thetemperature is a room temperature (20 degrees) and when the temperatureis increased by 20 more degrees.

TABLE 28 20 DEGREES 40 DEGREES ENTIRE SYSTEM 20.89 20.90 FIRST LENSGROUP 35.70 35.72

This shows that change of the focal length is suppressed at the time oftemperature change.

Further, FIGS. 30 to 32 illustrate spot diagrams in the respective imagesizes (100 inches, 80 inches, 60 inches) when the temperature isincreased by 20 more degrees from the room temperature (20 degrees).

FIGS. 30 to 32 also show good imaging performance even at the time oftemperature increase.

Note that the values corresponding to the conditional expressions (3),(4), and (7) to (12) are as shown below and satisfy the respectiveconditional expressions (3), (4), and (7) to (12) in the case of thesecond example of the second embodiment:

-   -   Conditional expression (7): dnTP=5.1    -   Conditional expression (8): θgFP=0.6122    -   Conditional expression (9): dnTN=3.6    -   Conditional expression (10): θgFN=0.5947    -   Conditional expression (11): |P40d(h)−P20d(h)|<FP=0.02 or less    -   Conditional expression (12): 0.85×D=16.745    -   Conditional expression (3): TR=0.261 (in the case of short        distance 60 inches)    -   : TR=0.254 (in the case of standard distance 80 inches)    -   : TR=0.249 (in the case of long distance 100 inches)    -   Conditional expression (4): BF/Y=3.45.

Further, as illustrated in FIG. 26, the conditional expression (12) issatisfied within a range of conditional expression (11).

According to the projection device specified by the above-describedembodiments and the specific exemplary values, the image projectiondevice having an ultra-short projection distance, formed in a compactsize, and having high performance and excellent temperaturecharacteristics can be achieved by designating the appropriate glassmaterial for each of the positive lens and the negative lens inside thefixed lens group. While the preferable embodiments of the presentinvention have been described in the above first and second examples ofthe second embodiment, the present invention is not limited to thecontent thereof.

Especially, the specific shapes and values of the respective componentsexemplified in the first example and the second example of the secondembodiment are merely examples to implement the present invention, andit should not be understood that a technical scope of the presentinvention is not limited by these examples.

Thus, the present invention is not limited to the content described inthe present embodiments, and modifications may be suitably made withoutdeparting in the scope without departing from the gist thereof.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that within thescope of the appended claims, the disclosure of the present inventionmay be practiced otherwise than as specifically described herein. Forexample, elements and/or features of different illustrative embodimentsmay be combined with each other and/or substituted for each other withinthe scope of this disclosure and appended claims.

1. A projection configured to magnify and project, on a screen, an imagedisplayed at an image display element, the projection device comprising:a dioptric system including at least one positive lens and at least onenegative lens; and a reflection optical system including a reflectionoptical element having at least one magnification, wherein therefractive optical system satisfies conditional expressions (1)-(3):4<dnTP,  (1)0.61<θgFP,  (2)3<dnTN,  (3) dnTP denotes a temperature coefficient of a relativerefractive index in an e line in a range of 40 to 60 degrees of thepositive lens, θgFP denotes a partial dispersion ratio in a g line andan F line of the positive lens, dnTN denotes a temperature coefficientof a relative refractive index in the e line in a range of 40 to 60degrees of the negative lens, and θgF denotes a partial dispersion ratioexpressed by conditional expression (4):θgF=(Ng−NF)/(NF−NC), where  (4) Ng denotes a refractive index relativeto the g line, NF denotes a refractive index relative to the F line, andNC denotes a refractive index relative to a C line.
 2. The projectiondevice according to claim 1, wherein the at least one positive lens andthe at least one negative lens are included in a lens group including alens having an aperture stop.
 3. The projection device according toclaim 1, wherein the at least one positive lens and the at least onenegative lens are included in a lens group closest to the image displayelement.
 4. The projection device according to claim 2, wherein at leastone of the at least one positive lens and the at least one negative lensis disposed closer to a magnification side than the aperture stop is tothe magnification side.
 5. The projection device according to claim 1,wherein the at least one positive lens and the at least one negativelens are included in a lens group which does not move in focusing. 6.The projection device according to claim 1, wherein the dioptric systemfurther includes at least one resin lens included in a lens group whichmoves in focusing, the at least one resin lens satisfies conditionalexpressions (5) and (6):|P40d(h)−P20d(h)|×FP<0.02,  (5)|h|<0.85×D,  (6) h denotes a height from an optical axis A, the opticalaxis A being an axis shared by a plurality of axisymmetric lenses of thedioptric system, D denotes a distance between the optical axis A and apoint where a distance from the optical axis A becomes largest amongintersections between a reduction-side lens surface and a beam, FPdenotes a paraxial focal length of the resin lens, P40 d(h) denotes amagnification when temperature at a height h from the optical axis A is40 degrees, and P20 d(h) denotes a magnification when temperature atheight h from the optical axis A is 20 degrees.
 7. The projection deviceaccording to claim 6, wherein the resin lens is included in a lens groupwhich moves in focusing.
 8. The projection device according to claim 1,wherein the reflection optical element is a concave mirror that includesa free-form surface.
 9. The projection device according to claim 1,wherein the conditional expression (7) is satisfied:BF/Y<4.0,  (7) BF denotes a distance from an intersection between asurface including the image display element and an optical axis A, to avertex of an image display element side surface of a lens closest to theimage display element, and Y denotes a maximum value of a distancebetween the optical axis and an end portion of an image forming unit,and the optical axis A is an axis shared by a plurality of axisymmetriclenses of the dioptric system.
 10. The projection device according toclaim 1, wherein a projection optical system is a non-telecentricoptical system.
 11. A projection system, comprising: the projectiondevice according to claim 1; and the screen satisfying the conditionalexpression (8):TR<0.30, wherein  (8) TR denotes a ratio of a distance to the screenfrom an intersection between the reflection optical element and theoptical axis A of the dioptric system, to a lateral width of the screen.12. A projection device configured to magnify and project, on a screen,an image displayed at an image display element, the projection devicecomprising: a dioptric system including a lens group and at least onepositive lens, the at least one positive lens being on a magnificationside of the lens group; and a reflection optical system including areflection optical element having at least one magnification, whereinthe lens group moves in focusing, the lens group includes a resin lens,the at least one positive lens satisfies conditional expressions (9) and(10) and the lens group satisfies conditional expressions (11) and (12):4<dnTP,  (9)0.61<θgFP,  (10)|P40d(h)−P20d(h)|×FP<0.02, and  (11)|h|<0.85×D,  (12) dnTP denotes a temperature coefficient of a relativerefractive index in an e line in a range of 40 to 60 degrees of thepositive lens, θgFP denotes a partial dispersion ratio in a g line andan F line of the positive lens, θgF denotes a partial dispersion ratioexpressed by conditional expression (13):θgF=(Ng−NF)/(NF−NC),  (13) Ng denotes a refractive index relative to theg line, NF denotes a refractive index relative to the F line, NC denotesa refractive index relative to a C line, h denotes a height from anoptical axis A, the optical axis A being an axis shared by a pluralityof axisymmetric lenses of the dioptric system, D denotes a distancebetween the optical axis A and a point where a distance from the opticalaxis A becomes largest among intersections between a reduction-side lenssurface and a beam, FP denotes a paraxial focal length of the resinlens, P40 d(h) denotes a magnification when temperature at a height hfrom the optical axis A is 40 degrees, and P20 d(h) denotes amagnification when temperature at height h from the optical axis A is 20degrees.
 13. The projection device according to claim 12, wherein thelens group moves from the magnification side to a reduction side infocusing from a long distance side to a short distance side.
 14. Theprojection device according to claim 12, wherein the at least onepositive lens is included in a second lens group that includes anaperture stop.
 15. The projection device according to claim 12, whereinthe at least one positive lens is included in a second lens group thatis closest to the image display element.
 16. The projection deviceaccording to claim 14, wherein the at least one positive lens isdisposed closer to the magnification side than the aperture stop is tothe magnification side.
 17. The projection device according to claim 12,wherein the at least one positive lens is included in a second lensgroup which does not move in focusing.